Some developers have been bulk publishing, according to Microsoft, which means they each are submitting hundreds of apps in just a few days. The apps meet all of the publishing requirements so anyone that has downloaded one, or several, of the apps don't have anything to worry about. Instead, the problem is it lessens the consumer experience when browsing through the store by pushing out other apps from the "New" category and filling it up with content from just a few publishers.
Unless you are publishing a blockbuster like Angry Birds, most apps have their biggest sales immediately after release due to the exposure in the "New" listing, where a lot of users go when they are browsing to see what the latest apps are. Some publishers are taking advantage of this and flooding the store with apps in a very short period of time. If you publish 50 apps and there are 200 new apps that day, you have a much better chance of getting one or more purchased versus a publisher that just published one or two apps.
Microsoft said they will still allow publishers to submit as many apps as they want, but only 20 will be approved each day, so if they submit 200 apps, it would take nearly two weeks for them to all become publicly available.
Honestly, if a publisher is doing this, they aren't in the market to create excellent apps and win a loyal following. They are just gaming the system. Microsoft has previously stated that where apps are concerned, quality was more important than quantity and this action backs that up. If it were just trying to catch the application stores for iOS and Android, it would love bulk publishers like this.
In somewhat related news, Microsoft stated that on June 15, 2011, it will officially cease accepting new apps for its older Windows Mobile 6.x platform. The platform's replacement, Windows Phone 7, hasn't been out a year yet. Anyone that purchased a 6.5 device late last year will no longer have any new apps to choose from in a few days. It goes beyond that though. Developers cannot upload updates, change prices, modify metadata, or any other information. Basically, it becomes frozen. Users can download it until Microsoft decides to kill the 6.x store or the developer requests the app is pulled.