Microsoft has made an announcement that will see windows phone users who dont upgrade their OS to windows phone 7.5 Mango missing a most inmportant feature. That of downloading apps from the marletplace. Users will only be able to browse through the apps, but purchase and download will be restricted to Mango users. Seems like Microsoft wants to fight the vice that is fragmentation in their OS. Access of Windows phone apps via Zune PC software will also be removed. Microsoft wants to reduce the number of platforms they ought to maintain offering the same service. Trimming, even though not in the scale like Google did last week with products that were seeming redundant.
Microsoft via the windows phone blog notes that with time they have learnt that most users get the apps from either the phone or the web stores, very minimally via the Zune software. However Zune HD app store wont be facing the axe. So it might be wise if you use apps (who doesnt?) you get the ugrade rolling, see how to do that here.