Respectfully disagree...this is the "App Store" forum and is where questions and reviews are for anything related to the App Store. Dev's want to get the feedback where users are going to check out apps and that is the app store forum. Users will continue to go and review and look for new threads related to apps here.
Now what could be done is have the moderators police it up. If there are no reviews when the promo's are gone then clear out the thread. The mods could also do a better job of consolidating like apps since posters are not likely to search any better.
I think two forums for the same app would be pointless and have users double posting.
A sticky would be acceptable but not another forum just for promo's