That's my point?
It's not about leveling. It's about progression. And that means the old-and-ancient "level 1 to 60 to begin the actual game" model is really not important, and can be replaced by any number of alternatives.
Doesn't really matter.
Not only is "people I know" a completely irrelevant and inherently biased metric, but you don't even know that they'd ACTUALLY quit; at best you know they say they would, and that's with not having seen or experienced whatever alternative there'd be. That's about as specious as it gets.
Even then, some people quitting is okay. Happens all the time. You can't make everyone happy. If the classic, traditional leveling model is a deal breaker for them, fair enough. There'll be other people.
It's SOMEWHAT important to SOME people, and we can only speculate as to the reason - given historical precedents for this kind of change, "I like tradition because it's tradition" tends to be a very common phenomenon. Experience has shown that once people actually witness a new paradigm first hand, then quite often it turns out they're not nearly as unwilling to change their mind as they claimed before. It's always the same with upending the established order: there's some die-hard conservatives and reactionaries, but for changes that make sense and are objectively justifiable, time tends to smooth over ostensible objections real fast.
But then again: I specifically said it's probably too late to change this in WoW, for various complicated reasons. That doesn't mean I don't think it's a better way of approaching game design.