New research into the Android Market and the iTunes App Store suggests that a whole lot of apps eventually get pulled from those store, as high as 37 percent of them in the Android Market.

TechCrunch has the story, which references a new report from research2guidance. It found that almost two in every five apps get removed from the Android Market after they’re published. But while it sounds like that could be Google cleaning house as problematic apps make their way into the Market, it’s actually more of a function of Android’s openness. Developers put out a lot more trial, marketing and potentially sub-standard apps into the Market, because it’s not as tightly regulated as, say, Apple’s iTunes Market. Then later, devs pull those apps in favor of better ones. The study found that of the apps pulled from the Android Market, 78 percent were free, which could indicate that developers put more effort into paid apps but use free ones to garner interest or hold a place in the store.

In the iTunes App Store, research2guidance found that there also is a high percentage of apps being pulled, as much as 24 percent. The situation there is a little different, and the lower numbers can probably be accounted for by Apple’s much stricter rules about what is allowed in its store. But it also suggests that Apple is constantly culling apps that don’t belong in its store, for various reasons. And even though it goes with a “walled garden” sort of model, it still has plenty of apps that don’t belong in its store.

The report also updated the number of apps available on each platform, finding that the Android Market offers 319,161 apps, while the iTunes App Store carries 459,589 (although Apple claims the number is an even 500,000). Android developers, on average, have about six applications in the Market, whereas iOS developers have an average of four apps available.

TechCrunch speculates that at the current rate, and given that, as Google noted earlier this week, there are 190 activated Android devices on the market, the total number of Android apps could eclipse iOS apps sometime this year. In research2guidance’s report, it found that about 500,000 Android apps have been published in total, while in the iTunes App Store, 600,000 had been published in total (with the removed apps accounting for the difference).

But the straight numbers don’t quite account for some of the other issues the Android Market faces. Yes, there are a lot of Android devices out there, but developers find better results working on Apple’s iOS platform because of issues like fragmentation and app discovery in the Android Market. That doesn’t mean that Google can’t fix or help those issues and propel the Market further, but at the moment, developers are drawn to iOS because they have more success there. Google has to address that issue before it will really be in a position to become the premier mobile platform for developers.