The Wall Street Journal reports that some big iOS developers are having a real issue with Apple's limit on testing devices. According to the App Store rules, developers are restricted to 100 devices for testing via ad-hoc distribution. That may sound like a lot (and it likely is for small or individual developers), but it makes large-scale tests of beta or preview applications difficult. Instagram, for example, is cited in the article as bumping up against the limit so much that the company bought a separate developer account, just for another 100 devices to be able to test on.
There are alternatives. TestFlight is an app testing service (which we've used) that allows developers to send out and update apps being tested on the fly*. Other services, like Pieceable, use the iOS simulator built into Xcode to deliver app beta builds over the Web for testing and feedback purposes. Not all the features work in that mode, but enough is there to let testers get the feel of the app.
Apple's enterprise developer program works to a different standard, allowing an unlimited number of employees to download and use apps. Of course, that's meant for enterprise software, not necessarily testing of standard consumer apps, and Apple's rules are clear that only employees of the organization are supposed to be licensed for the enterprise apps.
It's not clear whether Apple sees this as a big enough issue to start changing the rules. While there are more and more scenarios where wide beta testing pools would really help developers, I don't know if there are quite enough, in the larger picture, for Apple to change its tune -- noting that any expansion of the ad-hoc rules will make it easier for some developers to skirt the App Store (and Apple's 30% cut of revenues) entirely. It's more likely (and we've seen some of this already) that developers will change their process, perhaps even using some early post-release time to test and iron out their various apps and games.
*Update: Developers remind me that TestFlight still uses up developer UDIDs, so it's not actually an alternative to Apple's program, just an easier way to go about it.