People like analogies. Sometimes they're appropriate. Sometimes they're not. Take iOS and Android as an allegory for Mac and Windows. It might be superficially similar but that's as far as it goes.
IMHO tablets are similar. Android is, without question, a stunning success in the phone world. As is iOS, which singlehandededly transformed the mobile phone industry. People expect the same pattern to repeat in the tablet world.
I disagree. There are several fundamental differences:
1. Phones have a specific purpose, which for most people is the ability to make phone calls, send and receive text messages and use maps. I would guess that these are the three biggest uses of smartphones (but it is only a guess).
What's more, I think these account for the majority of actual usage. Apps are of course important but they are an add-on. Some people will use their smartphones almost completely app free (seriously). People I think forget this too.
Tablets are a different beast. There is much less inbuilt and obvious functionality. Apple has a vision of what the use case for this. I don't think anyone else really does (yet).
The ecosystem then becomes far more important and it's Apple with the music, movies/TV and, to a lesser extent, books (mainly due to Kindle, which is cross-platform). Android simply doesn't have this ecosystem so the use case for Android tablets for most people is a much tougher and less obvious sell.
I just don't see Android tablets (or any non-iPad tablets for that matter) gaining serious mass market traction for years to come.