I suspect the decision not to support Java on Maemo only became an official/concious decision once Qt became the official platform of choice for high end devices - prior to the purchase of Trolltech there just weren't the resources to get Java on to the first Maemo devices, and once Qt was chosen then supporting Java (even with Qt/Java bindings) became less important.

Highly doubt it was anything to do with legal issues since as you point out Java was already available on lower end Nokia/Symbian devices.