The game is most definitely not a 35-hour playthrough just to reach the final boss without 100%. I've played many story driven games from RPGs to shooters that don't even come close to this. A platformer certainly isn't anywhere near as time-consuming as those.
Then again, it all depends on your playstyle. If you're a platformer newbie, and you have no idea what you're doing or are just plain bad, it will take a lot longer to finish. For veterans like us, however, it won't be quite as difficult. 10-15 hours for a non-100% playthrough sounds much more reasonable.
(POTENTIAL SPOILER HERE)??
Also, while watching the recent EGX footage, it was revealed that it takes one Pagie to enter the first world, only three to enter the second, and only FIVE to expand the second. FIVE. At that rate, it seems that not many Pagies will really be required to even complete the game.