Why I bought it: 
1.  It seems like it will be a little better than X3 and more features.  Also, more enhancements will likely occur.
2.  I want Cakewalk to be in business.  Even if it is only as good as X3 - this is a reasonable amount to keep the support going in my humble opinion.  
3.  I have always upgraded before and over the years it gets better and better.  If past history is an indication of future history, I am good.
4.  I trust that they have hear enough about my color option complaints, that they are good people and will do what they can.
5.  I can afford it.  If someone cannot afford it and they are happy with X3, then I can understand why someone would just stay where they are.  X3 is a great product.

Platinum has been good to me so far. 
 
But I hope #4 is in the works. At this point, I would like a "concentrate on high priority requests and fixes" period. The two for me being colors and rock solid MIDI implementation.

I have confidence in Cakewalk.  I have been with them for about 20 years.  

Agree about colors. It seems like the current ones are mixed In with Gray pixels and it just looks awful. I bought DP because of this.