GL2 is using a Model-View-Controller based paradigm (see
MVCnPHP). This architecture will ensure only the libraries and code needed to process the current request gets loaded and only when needed.
There has been talk on the developer channels of looking at breaking up lib-common.php in more libraries. The one getting the biggest momentum is possibly creating lib-html.php which would have all the HTML widgets from lib-common.php. Doing this is fairly trivial but time consuming because we'd have to move those function out of lib-common.php and change the COM_ to HTML_ in all the code that references them. Not impossible but a lot of work to say the least. Doing this we'd also have to find a way to provide backwards compatibilty to plugins (probably done with simple wrapper functions using the old COM_ names that call their HTML_ replacement).
More to come I'm sure...
The reason people blame things on previous generations is that there's only one other choice.