Compare the iPhone and Android.
The iPhone is a closed platform. Apple dictates the programming language and frameworks to use for developing software for the thing. It even maintains strict control over the deployment process through the App Store. Plus Apple forks one third of the revenue stream to go to itself.
The Android is a so-called open platform. Every developer is free to select their preferred programming language and framework, while Google provides their preferred approach in the form of a Python and Java SDK. There is an app store for the Android called Android Market, but developers are not hindered in any other approach for their users to obtain their software. I call the platform semi-open because it lacks a characteristic I am especially fond of: run-time access for not only the source code (including being able to modify it), but also to do all that while the software is running. As Smalltalk systems have been providing since 1972.
Openness can be a two-sides sword: in the case of Apple it clearly shows advantages because the average quality of the applications is markably higher. This is not because software developed for the Android is crappy in general. It is because it is so much more difficult to create a high-quality application on the platform, because it is open. As the developers of Layar have communicated, they have considerable difficulty maintaining their application on the Android platform because of the heterogeneity of the platform, especially on the hardware level. Remember: Apple not only dictates the hardware its applications should run on, but also severely limits the heterogeneity of it.
Openness goes as far as it goes. Also Google has its restrictions on the hardware and intermediate levels of the Android architecture, and I think it would be hard to put a metric on how much “more open” it is. In fact, both platforms should in my opinion be regarded as closed, and Googles “openness” regarded as a marketing hype.
But again, I am not so sure how bad this is. Closedness brings it rewards, clearly.