Open source is about software but most of the criticism towards lack of openness to Nokia in e.g. the thread linked above goes around hardware aka products. Nokia doesn't aim to translate the open source principles to product planning and marketing.
And this is one of the reasons why Maemo is quite open (at least compared to direct competitors) when it comes to disclose and discuss about platform details relevant to developers, but less about end user features and even less about unannounced device products.
Even that is overly optimistic; everything has to be re-written for the unique environment of Android.
Maemo's standardness is its main strength, the thing that sets the Maemo devices apart from all the rest. That's a standard Linux kernel under the hood, and everything is built on standard, open-source toolkits, so it is relatively painless to port stuff... Unlike the competition, which requires a complete development from scratch approach.