on what legal grounds?
reverse engineering, if following certain rules, is fully legal.
nokia's policy in the question of maemo6/meego has, imo, a lot of people made distrustful of nokia's intentions to protect customers' investments.
i paid a lot of money for a device i don't want to fall in the "no fixes/updates for crucial parts" trap with, as i have seen happen to other hardware (fully) supported by closed drivers only (have a look at amd/ati's policy against their customers who do not buy a new graphics adaptor every few months).

after all, clean room implementations of reverse engineered drivers are an important part of the linux kernel since its very beginnings -- and it allows nokia to abandon products while pointing to open projects continuing development.
nokia adopting open source is not a matter of doing good, but of reducing costs (what would be maemo.org for if not helping nokia cutting down costs of customer support?). and if open source projects help provide fixes/updates after eol, nokia gains customers (because they can always point to o/s projects prolonging the lifetime of the products) and saves costs.