Some of the brands you mention like Definitive Technology shy away from reviews online, especially by us since we measure products and tend to be more critical than others. Polk seems to place more emphasis on reviews in print and/or CNET though we haven't actively pursued them for reviews as of yet. We have found too many other appealing products to go after first.
As for Paradigm, Mark Aling (their Marketing Manager) flat out denied us any product reviews and we have a whole thread about this. We noticed a pattern with that company in that they seem to only submit products for review in the magazines they advertise in. Kinda strange since we operate opposite in that we don't accept advertising from companies until we can verify they make legitimately good products.
See:
Status Updates on Paradigm Reviews