Yeah, it's probably not their equipment (they should be shooting with top-of-the-line cameras), but just their photography skills/style.
I have to be honest, I am not a fan of Photopass. The majority of the Photopass pictures I have seen or had taken have been blurry, poorly composed, overexposed, underexposed, etc... There have been a few instances where the Photopass shots have been acceptable, but for the most part they are average quality shots. As a few people have already stated, the more you learn about photography the more discerning you become about the photos you view. Before I go any further...I consider myself a photography amateur. I still have much to learn...please keep that in mind as you read the rest of this post.
I respectfully disagree with the assertion that Photopass photographers should be shooting with top of the line cameras. Many of the Photopass photographers do not have much, or any, real photography experience. I think most us agree that simply putting top of the line bodies and lenses in the hands of these folks won't automatically make them better photographers.
More importantly...think about the majority of Disney's customer base that actively purchase the Photopass service. These individuals are happy with the photos being purchased. Let me clearly state...it is not my intent to insult anyone who is a satisfied customer of Photopass.
My point is those individuals that are pleased with pictures taken by Photopass Photographers are likely folks that do not think about composition, the rule of thirds, accurate white balance, picture sharpness, aperture, shutter speed, and ISO. These folks simply want snapshots to memorialize their visit to Disney. And there is nothing wrong with that... These folks don't care if the shot is partially blurry, they don't care that everyone seems to have yellow skin, or green hair, or the fact there are shadows on the face of subjects wearing hats, or that the sky is totally blown out.
The aforementioned items are not important to most folks...therefore, from a business perspective, I do not see see the benefit purchasing higher end bodies for Photopass photographers. Their core audiences is happy with the pictures taken with D90's. Disney's financial folks would have ponder the benefit of incurring the expense of purchasing Nikon D800s / Canon Mark 5D Mark IIIs or Nikon D4s / Canon EOS 1DXs. These top of the line bodies run from $3,000 - $7,000 a piece. And then you have to purchase high end glass to really get the most out these bodies. Some of the top end glass will cost you $2,000+ a pop.
Another thing to consider, is that the cost associated with upgrading to high end bodies would then be passed on to the consumer. Currently Photopass is not what I would call an inexpensive service. I can only surmise that costs associated with the Photopass service would drastically increase in order to cover the acquisition and maintenance costs of the new equipment.
At the end of the day I'm not sure it would be a good business decision for Disney. And more importantly, I'm not convinced the majority of Photopass fans have a problem with the quality of product being offered and sold.