I'm sorry, but I have enver heard of the 100mm standard. I'll give them props for making them thin, but 100mm? 92 or 120 please...
Check the doubled holes in each corner - the outer ones are 100mm, the inners are 92mm. Not sure how much difference the extra 8mm makes, but as long as you've got a little clearance around the fan hole, these fans will probably go in without much trouble.
Conventional wisdom is that more blades=more static pressure (although there are lots of exceptions to this rule), so they're probably trying to compensate for thin fan. But yeah, more noise is a definite possibility.
i7 2600K | ASUS Maximus IV GENE-Z | 580GTX | Corsair DDR3-2133