I think that it's more likely that we are seeing "caffeine style" tweeks within the framework of the current algorithm. So that when caffeine does become fully deployed, the changes won't be as noticable and there will be less disruption to the SERPS.
One of the major components of Caffeine is a rewrite of the Google File System (GFS). The new GFS2 will give Google the ability to index more pages and speed the time that the pages are searched.
Why the need for more power and speed? Phrasification and phrase based indexing.
Google Inc US Patent: Index server architecture using tiered and sharded phrase posting lists
Google has just been awarded a patent for phrasification which "compares the phrase's score to a second threshold, which is used to further identify strong phrases. If a candidate phrase has a score above the strong phrase threshold, it is determined to be likely to be a real phrase, and thus the phrase's score need not be further devolved to its subphrases."
"clustering may be used to decide which pages to show in search results in what order based upon the phrases included in a search query, and phrases that are related to those query phrases"