'Twas brillig, and the slithy toves did gyre and gimble in the wabe

Okay, I'll accept the one about Outlook Express. Though I don't recall Windows Live Mail (or whatever it's called in Windows 7) behaving that much differently to Outlook Express.

But with Facebook and LiveJournal, while they can't run multiple versions of the site there is a significant difference in how the two sites are run. With LiveJournal, the look and feel of the site up until recently (I'm aware of the current grand redesign) has been largely unchanged, and while they've added new features they've done so in a way that doesn't break existing behaviour. Facebook, on the other hand, keeps on rearranging the site every time they add a new feature and in the process usually breaks whatever existing feature is being replaced/superseded/enhanced. Livejournal also announces new features via the news journal which all new accounts are subscribed to, while if Facebook has an equivalent it certainly doesn't notify you by default.