This is only my opinion, but I have been around since the early days so it may be worth the obligatory 2 cents.  First, I will acknowledge that the DotNetNuke Marketplace is a viable storefront that some developers of skins and modules have already taken advantage of.

For the most part, I think the reason you see more releases of skins and modules on Snowcovered is because the developers and designers are sticking with what works for them.

We have been selling on Snowcovered for a long time and it has been working for us.
We are familiar with the process, and the tools available, and have seen them grow based on our feedback.
Having to go through any certification process is just another step that takes time away from development and support. As pointed out, the requirements are not that tough, but my perception is still that the benefits of being "reviewed by DotNetNuke" do not provide enough value of having to pay for a process to be listed in a store that does not offer any more benefits to me as a vendor.

Also, after paying to be reviewed, the DotNetNuke Marketplace still wants 25% commission on products sold.  I think that is a steep price for the "new player" to charge module and skin developers without any real added benefit.  Snowcovered also gets 25%, but I see a big difference in how that 25% gets reallocated.

Here are some key differences as I see them today:

• Developers who have products listed on Snowcovered get 10% off when they buy products on Snowcovered.
• Snowcovered offers a 10% referral fee to anyone that links to their store and have done so since they started, even if you are just linking to your own product. This means that the 25% is easily reduced to 15%.
• Snowcovered has built a ton of loyalty with their customers and developers by always responding to both with new and innovative ways to address the needs of both.  DNN Corp. may do the same, but they have to play catch up.
• The listing of your product on Snowcovered is very liberal which produces the affect that the service is purely a third-party connecting the customer to the vendor.  Vendors can update their own profiles and Listings with links to their own sites. Vendors can manage their own support or use the very robust system built into the service.  I can't speak as a vendor or customer of the DotNetNuke Marketplace, but I do not see any links to the actual vendor sites to help me decide what kind of support I can offer my customers.
• Submission to the DotNetNuke Marketplace is through a formal process that takes a lot of time, mainly because it is filtered through a single person performing that process.  The submission process on Snowcovered has been fine tuned over time and is very efficient.  There is a lot of time and effort that goes into packaging a real product for retail sale, the last thing we need is to wait weeks to get that product through a formal process that may be delayed for any number of reasons.
  

The last item is actually used as the value statement for the DotNetNuke Marketplace.  They claim they are raising the bar for the commercial DotNetNuke Modules ecosystem by providing that process and thereby increasing consumer confidence when it comes to buying modules.  As a purchaser of many, many modules I disagree.  I have seen the process from both inside and out and I have been a part of the commercial market of DNN as a consumer and a vendor.  In my opinion, you can get a better review by doing your own research on any module or skin you are thinking of buying.  And that review is a lot easier to do if I have fast access to the vendor's support system.

All that being said, since DotNetNuke Corporation has the ability to push their advertising out with the application then it is probably only a matter of time before more and more developers will start moving to where they can get that added exposure.

Sorry for rambling on, but I think it is a good topic, and to keep it going I have a question;

Will the Snowcovered store be added into the new solution explorer?  Should it be?

Ok, I guess technically that is two questions...  But hey, I did give 2 cents before asking. :)