I believe the answer will be that it takes less time and fewer resources to update X rows in a narrow table than it does to update the same X number of rows in a wide table because the pages being updated do have to be read and a page is the smallest amount of data that can actually be read. So, the more narrow the table, the more rows you can fit on a page, the fewer the number of pages that will need to be read.
--Jeff Moden
Change is inevitable... Change for the better is not.