Actually its Nokias learning curve on what maemo is capable of when given to a larger tech oriented audience. I imagine the reason behind that would be to do exactly what you mention. Learn before maemo 6 and a consumer device comes out.
Nokia pour by far and away more money into research etc than any other device manufaturer and its obvious the investment in maemo as a future OS for their upcoming lineup is something that is long term and important (see articles regarding Nokias statements about the sunsetting of s60). Maemo 6 will be built on the lessons learnt here and now and will have the advantage of being fully QT 4.6 alowing devs to write once run many places. No other device is even close to that (and please don't say Android does that because it doesn't).
After the debacle that was the last release Nokia could have simply gone back to a boring old safe s60. Instead the chose to go all out and try revolutionise the field.
Remember man. Great innovation takes great risk.