A tragic incident indeed.
Thankfully, severe injury and death as a result of being struck by the ball is extremely rare. Statistics seem to suggest that the vast majority of on-field fatalities during cricket matches are as a result of a player suffering a heart attack.
I played a lot of cricket when I was (much) younger, and umpired a fair bit since, and the worse directly cricket-related injury I've witnessed was a broken jaw when a batsmen was struck by a vicious short-pitched delivery. As it so happens, I was the bowler, and I still remember the feeling of cold terror that swept through me when the poor chap went down. With less serious injuries and glancing head blows, the batsmen may often stagger around and try to keep on his feet, or just sit down and try to regain his composure. But this guy went straight down, he was out cold before he hit the deck. Thankfully he came round really quickly, and was taken to hospital. The fracture wasn't serious and he returned later on that afternoon.
This was at a time when a fair few pros had started wearing helmets, but they were still a rarity in League cricket. In the situation I've described above, a helmet with a front grille would have almost certainly prevented the batsman's injury. It's good to see that helmet wearing for batsmen has been compulsory for players under the age of 18 for a while now.
Mind you, having said that, I often wonder if, to a certain extent, the wearing of helmets and increasing amounts of protective padding is something of a double-edged coin. For most of cricket's history, the only additional protection afforded a batsman would have been steel toe-capped boots, leg pads, a box/cup, and maybe a towel fashioned as a crude thigh pad.
With the head (especially) exposed, I do believe that two significant factors in these pre-helmet, pre-body padding days helped contribute to the extremely low rates of fatalities and serious injuries in the game (at all levels).
Firstly, batsmen were forced to rely on good technique to avoid getting struck by the ball. Batsmen are always taught to watch the ball until the last possible moment before deciding on whether or not to try and play it with the bat, or to take evasive action. It was drilled into us time and again that the worse thing you could do against the short-pitched delivery was to turn your head away. I would say that of the two options of trying to play the ball or avoiding it, those following the avoid technique were
much less likely to get hit. And from experience, I'd go as far as to say that those batsmen attempting to hit the short-pitched ball (most likely playing a pull or hook shot) were far more likely to get struck by the ball after they'd made some contact with it with their bat (a top-edge or a bottom-edge) - in other words, good footwork and head position meant they were unlikely to have been hit directly as a result of missing the ball completely.
Tragically in the case of Phil Hughes, it would appear that, although it was a 'freak' hit on an unprotected part of his skull, he had actually turned away from the ball before it struck him.
The other contributing factor to the relatively low frequency of head and upper body injuries in the days before helmets was a code of conduct known as "the fast bowlers' union". As a very general rule, most fast bowlers are not good batsmen, and are therefore likely to be the least capable at avoiding being struck by fast short-pitched bowling. To these ends, it was an unwritten rule that fast bowlers simply didn't bowl fast short-pitched 'bouncers' at each other. It was also considered incredibly unsporting - literally
just not cricket - to bowl dangerously at younger players and anyone who it was obvious were not up to the task of adequately protecting themselves. These 'rules' still hold good in a lot of amateur cricket, even when the less-able batsmen are wearing high quality padding and helmets.
As a slight aside, it's not just this specific attitude toward voluntarily trying not to endanger weaker players that has been deliberately coached out of the game. At one time, even most test players would always 'walk' if they'd knowingly been caught behind, even if the umpire hadn't given them out. I remember there being a few well-known 'non-walkers' around when I played - although they were of course under no obligation whatsoever to declare themselves out, but to wait for the umpire to make a decision, they were always thought of as 'cheating' to a certain extent; their actions were considered well within the laws of the game, but certainly not in the
spirit of the game. There are a few other technical incidences that fall into the 'spirit of the laws' category that have been consigned to a bygone day, such as the bowler running out the non-striking batsmen, although I think by far it is the fast bowlers' union and the not 'walking' examples that have changed the game the most.
Sadly (in my opinion anyway), this sporting attitude has now been completely lost from the game, from league cricket all the way up to test level. I suppose the 'win at all costs' approach was bound to gain popularity as more money has come into the game. I would argue that by far the biggest factor in this change were Kerry Packer's World Series events; although players had always been encouraged with small win bonuses, the majority of their onfield income came from domestic cricket, and they would receive just a basic match fee for test matches. Packer changed all that. Although I believe what he did in ensuring future generations of cricketers would be paid 'properly', unfortunately there a was a small but noticeable shift in emphasis away from cricket as a form of entertainment to cricket as a totally results-led enterprise.