Not all record labels need to attend because there's a lot of global press coverage of the SXSW festival. And also for example, bands from as far north; Seattle, Minnesota and Wisconsin all got excellent local news coverage.
There is also music, film and game awards for example; Austin local's "Riders Against the Storm" won this year's "Band of the Year" award.
Most bands who previously performed at SXSW will plan way, way ahead (get rooms and travel arrangements done, and if later on the band cannot play? There's still plenty of time to cancel).
A lot of acts probably use backing music and/or use the backline gear already supplied. Point is; the focus of these events is all about PR, PR, PR, coming up with clever strategies to maximize media coverage of what is a BIG music festival that is well known worldwide.... Sure, not all record labels attend, buy hey, they don't need to attend because they will most definitely read all about it
Having great songs, tight performances and sound is only half the battle. Clever PR, good relations with press contacts is paramount, this is key to success, followed by.... oh yeah, the record label... say what? THE RECORD LABEL, oh... yeah that :P

. A great band can achieve success with an "
Independent Label"
There's a lot of good information (and unfortunately misinformation) about PR strategies. Mostly, it's about 'how to' rather than how much money (beware of scams)!
The car incident that killed; deliberately mowed down those people was shocking, very sad news. My thoughts go out to family and friends of the victims. BIG events such as SXSW requires local police and security to be much better prepared and organized in regards to safety and security of everyone attending 'such events'; i.e Austin or anywhere else.
@ Spindlebox,
It's been a long time (over a year ago) since I heard your music. So I headed on over to your website for listen; Alice Sweet Alice "Great songs, performances and sound." Keep up the great effort, wish you all the best!