Hey there!
Yep, Premiere Pro is limited to 4 “live” streams at any given point in its multicam feature, which I hope they will fix with the upcoming release of CS6.
For now, I suppose one course of action is to run multiple multicam sequences four streams at a time (I haven’t done it, so I’m not sure how effective it will be, if at all) and then put all the edits into a final sequence. It’s time consuming, but would still be faster than doing it all manually.
As for your surprise, for years Adobe neglected Premiere but with the demise of Final Cut Pro (and the rise of iMovie Pro), that is changing for the better!