Condesension aside, yes, 4e was pretty simple. It has a single class progression, a common structure. I've seen it deeply confuse experienced gamers, because they keep looking for complexity that simply isn't there. That's why I was surprised by Essentials trying to be 'simpler.' I mean, there's only so simple you can get before you're playing candyland or something.
'Simpler' wasn't really what they meant, though. As has been pointed out. Essentials is retro, and in earlier versions of the game, some classes were 'simpler' than (inferior to) others. Specifically, non-casters were simple compared to casters - and casters could be more thoroughly abused to achieve game-breaking power. While having mechanically different classes with varying degrees of complexity delivers 'simplicity' to a few builds, it makes the whole system more complex - more daunting to new players trying to take it all in, and more amenable to 'rewarding system mastery' (powergaming, optimization, rampant munchkinism, whatever you want to call it).