Sure people can fool you with washed-up phrases like “there’s no I in TEAM” and such, but the truth in the design community is a little different. Actually the more people involved in a project, the more fragmented it will be. Think of it as an android headset, with all the resolutions, different processors and performance, and a design needs to now fit it all.
With iPhone’s it’s a bit easier – there’s the iPhone (sure, two resolutions, but that’s easy – just double) and you can create something for it actually being sure it will look and work the same. Well let’s not jump into that analogy too far, I hope you got it. The more people involved, the less stable the design is. Thus the best teams are usually the smallest.
Thinking about the successes of recent years in mobile apps and games, (well aside from Rovio) most of the biggest, most creative ideas came from small, 2-3 people teams. Sometimes it can even be a one person, and then the vision is completely as it was imagined from the beginning.
Is it even possible to create something good with a team larger than two people anymore? Well we just need to wait and see.