Hm, I never had issues with that. Maybe if you use Chrome since that runs pretty terrible on OS X, but otherwise no issues. OS X tries to keep your memory pretty full, since there is no point in having a bunch of memory if you don't use it.
When used Mac OS X for an iOS project, it was hardly an issue, just something I happen to see sometimes being posted, not sure how serious it really is.
Otherwise I spend my time in other systems anyway, so I cannot properly judge it.