I'm pretty agnostic towards micro-controller manufactures. As long as I can program in a higher level language then assembler and the chip is fast enough and has enough memory and hardware features and affordable, I can be 'converted over'.
I just think the Arduino folks were the first to build on all open source tools and IDE, multi-platformed, and threw in open source hardware to boot. I'm happy for their success and really enjoy their platform. However I don't think they are the only path to happiness, now and into the future. Let competition do it's thing and let the customers vote with their wallets, I say. 
Lefty