I think there is a big difference between banning it outright (like Apple) and hampering it. From the end-users point of view both suck, but at least if I use Firefox to sync my bookmarks and passwords I'm able to on a Windows tablet. Nothing I can do on an iPad.
First, let's assume the majority of users are not going to know why the an app is not allowed and/or why it is sluggish/limited/hampered/etc. From the average user point of view... the biggest difference to me is that when it is banned, the banner (Apple) is the bad guy for not letting it in. When it is severely hampered the bad guy appears to be the creator (Firefox) for making a crap app when in reality the hamper-er (Microsoft) is the bad guy for crippling the app's ability to perform as well as it can.
