Well, yes, ideally they should be, but sometimes they aren't, especially when the presenters use high-quality photographs to stress their points. Or, if you are an Apple Keynote user like me, you export the slides to PDF to be able to upload them to SlideShare. This happened to me last week when I was trying to upload several of our CTO's (who I work for) presentations. I eventually got them all up into SlideShare, but one of them took a bit of work. The PDF file came in at 43MB. After trying a couple of things, I queried my Twitter network and got back a great number of suggestions. Ultimately I learned about the Automator tool built directly into Mac OS X and soon had a little script going that solved my problem.
The point is that all of that took time, which I didn't really have for my "Oh, I'll just upload the 3 presos to SlideShare" side project. (And then of course once I couldn't do it I just had to figure out why not and how I could.)
So I'm delighted that SlideShare has raised the upload size - thank you!
P.S. And yes, the other things they mention about seeing the number of embedded views, including videos in replies, etc. are all interesting, but not as exciting to me as the upload size.