My reasons for this are:
- When you have a bug in your installed version, there's no guarantee that it will be in the debug portable version, or that you'll be able to set all the settings in the debug version like you did in your regular version a while ago to replicate the nasty bug.
The only thing you know at that point is: you're having a bug in this specific installation and you'd like to get it fixed with as little frustration as possible. And installing and setting up a debug version seems like a lot of frustration to me just to help the developers fix their own product, if you're not getting paid for it. - The current state of things divides the users into hardcore teststers, that always have the debug version handy, and those who won't ever be arsed to help any living thing on this planet. But what about those who don't usually do testing/debugging, but when they have a bug, could help, if the helping process isn't too cryptic?
- It not only would be more convenient for the on-spot debugging, but, I'd imagine, for packaging and releasing, too.