What? The roads are LINES. Why would they 'change'? I'm not sure what you mean. The shape of the country is of course the same as the old maps, islands or no islands. And there WERE no islands on the shore in other maps. And there actually aren't any now. Those 'Islands' are just ice, you can tell because they just off, white, from the mainland. And why do you think they're big? Maybe they are really tiny. Cyrodill had some small looking islands on it's map http://www.xbox365.com/gdb/images/GGdLLHLdPP02202340/Oblivion_22_500.jpg and guess what? They were tiny!
There's no reason whatsoever from that 'evidence' to suppose the game map will be huge.
here... http://www.google.com/imgres?imgurl=http://images1.wikia.nocookie.net/fallout/images//e/e8/Wastelandmap_notext.png&imgrefurl=http://www.neoseeker.com/forums/37659/t1256684-bobblehead-location-guide-spoilers/2.htm&h=1088&w=1088&sz=386&tbnid=ncUbnNfRXswORM:&tbnh=150&tbnw=150&prev=/images%3Fq%3Dfallout%2B3%2Bmap&zoom=1&q=fallout+3+map&hl=en&usg=__LRRTnIU2T1oxGhZigT5vuwXGdjs=&sa=X&ei=E2AsTb2-JomqsAOCvp2EBg&sqi=2&ved=0CCUQ9QEwBA
here http://buriedplanet.com/userfiles/fallout%203%20map%20complete.jpg
here http://fallout.wikia.com/wiki/Fallout:_New_Vegas_map
now remember fallout was bigger then ob.