They may be legally covered but they would literally shoot their whole network in the foot from PR standpoint if merchants have no code of conduct or a standard Terms of service. Handling affiliate signups in bulk gives the implication of some type of affiliate network even with their disclaimer on the site and (somewhat irritating) re-mention of that in any affiliate-related questions (even though my question regarded their software, not the merchant).
Maybe it's just my opinion but a strong base of affiliates should be one of the biggest selling points to merchants and could even take them out of competing purely on price - which is usually a losing business model. If I was a merchant and my shopping cart provider said, oh and by the way... we have a slew of top affiliates waiting to promote products like yours - you'll most likely make back whatever you pay us on from them alone, I'd buy in for sure.
At least require merchants to post a terms of service for cryin' out loud. It just looks sloppy and may get you in some legal hot water - even w/ that legal disclaimer, you know how the courts are these days. Plus the PR black eye would be disastrous.