First of all, get the 6.0b update for Vegas. Not saying that doing this will magically fix your problems but it’s better to have the current release.
As I see it though, your biggest problem is that the files are from a digital camera, not a video camera. This forum is one of many forums where people are trying to use and/or convert video that (I’m certain) the original coders never even thought of (Divx, & Xvid for example).
Sony is no different than any other manufacturer in releasing products that may not work with other products they build. They’re a huge organization and each division is completely separate. If I was to use your line of reasoning, I’d be complaining because Vegas couldn’t import files from their Cine Alta line of HD cameras. After all, Sony makes it so why can’t Vegas read it?
Bottom line in all of this is that Vegas is a great NLE for the formats it was originally designed for. If you try to deal with anything else, you will have to, as you’ve discovered, jump through hoops 🙁