Google Glass is much expected by both users and developers, but it seems developers won't be able to do too much with it early on, as Google has limited the API, and the development stack to only HTML5.
Google is taking the same approach Apple took with the first generation iPhone, when they tried to keep it as limited as possible, to try to control how its ecosystem will be shaped, and also because they initially envisioned an ecosystem of web apps for the iPhone, and not one of native apps. However, the developers kept asking Apple to allow them to make native apps for it, and they eventually did it.
Google seems to be doing the same, and even going a step further. They will only allow web apps that go through their cloud at first, most likely through a web store, similar to the Chrome web store. Developers can't even use custom CSS, and they have to use Google's own templates.
This also reminds me of how Apple created all the UI resources developers could use for their native apps later on, and this made it easy for just about anyone to make beautiful iPhone apps, because even developers who were bad designers could just use Apple's resources, instead of using less pretty designs of their own. This sort of attitude ensures that the web apps for Google Glass are of higher quality on average, even though they will be limited by what developers can do with HTML5.
But just like Apple, I expect Google to open up the platform later on, once they have a better idea of what can be the "killer apps" for Google Glass, and what's the best direction to take for it. That doesn't guarantee Google Apps will ever have native apps on it, though, especially if web apps become better and better in the future, and closer to native performance.
Google also doesn't want developers to go too crazy with their apps right now, and ruin the battery life of Google Glasses. For a device that you're supposed to use all day, and record a lot of video with it, or use VOIP/video calls with it, you need as much battery life as you can get, especially since it constantly needs to be connected to your phone through bluetooth, and it doesn't even have a lot of space for a battery.
I think this is the right approach to take not just with Google Glass, but with any sort of product. It doesn't mean it should stay a closed platform, but at least in the first 2 years or so, it needs to set certain standards and expectations for both developers and users.