Neither MW or OB (havent played others) did not end with the MQ, and skyrim wont either. that means any quests not completed after doing the MQ will (should) remain available. its an open world rpg remember. *glares at Obsidian*

Nobody has questioned that, all I am saying is that after finishing the MQ the world feels empty and kind of dead, and your further actions seem to have no real purpose.

the op suggests that theres nothing to do after the MQ, or that the world seems empty, but thats not really the case. There will mostlikly be guild questlines that are not essential or linked to the main quest. I seriously doubt we will even be forced to do the MQ, I didn't even finish MW MQ until just a year ago, and Ive been playiing for about 4-5 yrs.

you could just rush the mq and do every thing else afterwards, or wait for the main quest to do last. thus my restating that it is an open world rpg.

The OP doesn't suggest that. Read carefully:

"Sure, you can still do sidequests you haven't done before, but a thing that always distracts me is that a world which you just saved from its utter doom remains exactly the same as it was before, except for maybe a few new dialogue lines. "

In a lot of games where you can continue after finishing the mainquest, the game just feels "empty" when doing so.
A few examples are Fable 3 (which can even become empty in the most literal sense), mass effect 2, or Fallout 3 (without dlc).

Sure, you can still do sidequests you haven't done before, but a thing that always distracts me is that a world which you just saved from its utter doom remains exactly the same as it was before, except for maybe a few new dialogue lines.
So normally, after playing through the game's mainquest, I tend to stop playing it even though there are still a lot of sidequests left.

What I would need to keep me going was new possibilites to open up. For example, after finishing the mainquest you can become duke of a city, get a castle which you could costumize, hire servants etc. Another way would be to open up tasks that keep you motivated, for example you get a map with certain items that you could combine to build a new sword, or you could get the task to kill off all remaining dragons/werewolves and stuff. Of course, the NPCs should react to you as their saviour properly and treat you with respect and esteem.

What do you think?

First off let me say that I love you site and that extra creditz is what makes my week. Second I would like to say that I agree, I think that after I save skrom's ass that the world should change with new quests