Currently one of the major feature which is lacking in Android is Auto update of the OS itself. Currently OS updatability is depended on the Mobile Manufacture + Mobile Operator which is like 2 edge sword.
Hence you are normally stuck with the version of Android with which the phone was shipped and most of the vendors will not worry much about upgrading it. Mobile industry is one of the fastest growing in software sector thanks to smart phone OS war. As of now Apple and Windows 7 (which came late into the game) have an upper hand in upgrading the OS of the mobile and have direct control over it.
I hope Google does something about this issue and resolve it asap, till than I am stuck with Android 2.1 on my phone 🙁