It's a bit different though -- if you look at stats on Flurry for some of the popular apps, you'll see that there is less than 3% iPhone OS 2.0 users out there. That's simply because iPhone users get a free OS upgrade when they hook up to iTunes. The majority of users who are still stuck in the 2.0 land are iPod Touch users since they actually have to pay for the 3.0 upgrade. That's why the iPhone market has significantly less fragmentation.

However, I have a HTC MyTouch android phone that is still stuck in 1.6 land. I upgraded from 1.5 recently, but it was not the simplest process to do so. HTC doesn't really make it easy for phone owners to upgrade their phone OS. It's possible for me to use the CyanogenMod to upgrade my OS to 2.0, but not without lots of effort at the command line.

The current slew of 1.5/1.6 android devices out there right now will probably never be upgraded to 2.x mostly because the phone manufacturers rarely make it an easy process.

People don't seem to notice that on the iPhone platform fragmentation is limited because people keep buying new devices.

Usage stats from my app in April (somewhat unscientific but illustrates my point decently): iPhone 3G: 49 users iPhone 3GS: 48 users iPod Touch 2nd Gen 4 users iPod Touch 1st Gen 3 users iPhone Edge 2 users iPod touch 1 user iPad 1 user (might have been me...)

Well, the 2G is being phased out with the next OS release, meaning that even though people will still use their old one development will still be focused on a few core devices. The first major fragmentation will be with the new hi-res screen on the next iPhone, the 3G and 3GS aren't really that different to develop for.