Excuses, excuses. They are using a very power efficient 4 year old processor type with a 1500mAH battery.
All widgets can be updated with one polling operation. Certain widgets can define their own update schedules. There can be some amount of intelligence applied to such problems. The thing is that Nokia these days does not have enough and so they can't apply any to their products or software.
I have MFE running push e-mail all day and even on the battery hungry N95 I go through the day. Something like Facebook which needs constant updates like MFE can run without killing your battery. If anything offer users CHOICE.
I, as the user can decide whether I want 15 widgets and make my OWN determination that I would like to trade off some widgets for more battery life or vice versa.
I don't need these clowns to hold my ****ing hand and tell me what's good for me. They were just too lazy to implement multiple home screens so while the Nokia clown himself just said "no" to the question without any further explanation, count on the fanboys making up the excuses now.