If you have access to the CC versions of Sg, you've also probably got access to PrPro. The way the Adobe stuff is designed is that PrPro is sort of the 'entry' program for footage. It handles nearly every codec except some of the RAW formats and most variable-frame-rate stuff (cell phone 'footage' et al). Or you can say use Adobe's Media Encoder (also on the CC list) and transcode to take either AVCHD or MP4 footage into perhaps DNxHD for grading into Speedgrade without using PrPro.
Speedgrade's design team works on the grading end of things, and kinda figures that PrPro & AME can do the heavy-lifting to get other codecs into a usable form. Like many folks these days, I use both PrPro & Speedgrade ... so I load a project into PrPro, start some basic editing ... and the direct-to-Speedgrade link is so fast that I'll take even just sections or clips from sequences at times and run over to Sg, check out what they grade like ... then go back into PrPro. Takes seconds each way. And that way, ANY format that PrPro can use loads into Speedgrade without a hitch nor hassle. No XML files, no EDL's, no DPX, no transcoding ... slick as anything.
So, no, it isn't actually completely ridiculous ... though it can be a bit annoying. Look at the files Sg handles "native" ... things like RED, Arri, Alexxa, that sort of thing. That's because it's designed to do dailies with the most heavily used major cameras for large projects. I've always kind of wondered, as many tv stations as use cameras that shoot AVCHD, why that wasn't on the list but oh well. They figure for "regular" work handling things coming in from a PrPro project works great, and why re-invent the wheel when it works just great in PrPro?
For grading, Speedgrade is an awesome program. Though I can certainly give you a critique of both where they've done incredibly well and where they, like any other human, could perhaps improve something maybe. And they have heard plenty of those comments direct from me ... and when I got down to NAB last March, they were still thrilled to meet in person the guy that complained so much. Really nifty group of people working on it.
So join the group ... and feel free to complain about things! Hey, the rest of us sure do ...
Neil