This is just a hunch, but I believe the fact that NAR has allowed Realtor.com to aggregate MLS data & syndicate all their listings is a direct response to the Zillow deal with Yahoo! Real Estate. Zillow will be syndicating all their listings to Yahoo! Real Estate, which means by putting a listing on Zillow an agent instantly gets it in front of 20+ million UUs (granted, obviously not all of those 20 million will see a particular listing).

Realtor.com realizes their sales team no longer has access to the largest consumer base since Zillow’s sales team is now selling Zillow & Yahoo! RE ad space — and Realtor.com likely views this deal with NAR as the way to gain the flexibility to put some partnerships in place to try to regain that top spot. As a result, I’ll venture a guess Realtor.com will not syndicate listings freely or even for a flat fee — I’m betting they will only do it if it also means their sales team can sell ad space on site X.

Disclosure: I worked for Zillow for 4 1/2 years – but have been given no insider knowledge on the NAR deal with R.com (or the Zillow/Yahoo! deal for that matter).