What specifically makes up a Mulching Lawnmower ie., special type blade, shape of body housing, etc.?

Can't say I'm a 'professional', but the inner deck is also part of the mulching secret, it creates a vacuum to suspend the grass longer to cut it multiple times., clean the inside of the deck and make sure your blades are sharp and without many major dings. If the decks gunked up or the blades aren't sharp your mower won't mulch well. Also the usual plug, oil, and filter replacement every year helps a lot. Almost forgot your other question. I believe that toothed blades are mostly for heavy cover applications more like making your mower a semi-poor man's twig chipper......

Mulching mowers have no grass exit, forcing the clipping to stay under the housing to be chopped again. The blade has some curves in it - not a straight design.

In my opinion, they are a poor design, and don't work!

the blade is what actually mulches,but the mower deck on a mulcher mower is deeper then a reg mower,this is to allow the clipping's to circulate and get chopped up better,also the underside of the mower must be kept clean to allow clipping's to circulate properly

I always try to stick with one brand, and my personal preference is John Deer. They have been wonderful and helpful (except in town South Florida Ave, Lakeland, Florida) manager are NASTY, so been dealing with the John Deer corporate directly. I have spent thousands for their equipment.