I would say it's relevent, but also must be interpreted for intent. Steve also said that nobody reads anymore, and the not too much later was hyping iBooks at a press conference. Steve once dismissed TVs by saying they were only for when you wanted to switch off your brain and a few years later he was hawking the AppleTV set-top box, and now Apple is rumored to be working on a TV of their own. Steve said nobody needed Firewire because all camcorders sold at the time used USB (apparently forgetting about all the ones sold before that), and less than a year later Apple put FW back on the laptops it was removed from. Steve said no buttons on the shuffle was a great thing...
The point being, sometimes Steve's comments are opinions, not to be interpreted as direction for Apple, sometimes they appear to have been to intentionally mislead, and sometimes Steve (and Apple) simply make mistakes. People give FAR too much weight to Steve's comments about 7" tablets. He was simultaneously promoting Apple's choice of size as ideal and at the same time demoting the idea of a smaller tablet in the minds of everyone who thinks Steve/Apple could do no wrong (and that's a lot of people).
And he's not exactly an unbiased observer making those comments. Steve Jobs was as much a marketer as he was a designer (perhaps even moreso). What would you expect him to say? "Well, the size we picked was just one option and other people will come out with other sizes that are just as good as ours because different people have different needs in a tablet." Hell no! It's "Ours is the only viable alternative and all the rest of the options are crap." That is the foundation of almost every marketing presenterion, er keynote address, Steve ever gave. Ever other exec says the same thing about their company's products, they just don't have Steve's style and flair.
Haven't paid much attention to the changes in the iPod and iPhone lineups over the years, have you? Apple doesn't care if Otterbox or other case companies have to change their lineups. In fact, those other companies probably like that Apple changes things with every new release. That way you need to go buy a new case from them, too, when you upgrade!
Um, then don't buy one. (PS: chill)