IMHO: Just because the ability to switch is not included does not mean that it may not make its way back at a late time in the form of a setting that can be enabled. Having it off by default may be a way to keep under the Google radar and appease the end user as well.
Regarding the limited functionality, android as it stands has a problem with keeping track of data in apps when they are not in the forground. Before Cornerstone I have found myself working in an Office suite, switching to an internet browser, then switching back only to find that the last few sentences or even the entire document have been flushed from Androids memory never to be found again.
Thanks to cornerstone working between complementary apps can be done side by side instead of one on top of the other.