tedster - 11:14 pm on Dec 8, 2012 (gmt 0)
No, it's not the exact list at all. It's just the top few synonyms that have the strongest statistical correlation. In fact, Google has a huge pile of data about semantic relationships and sometimes the SERPs themselves can be a better tip-off than the tilde operator!
The key discussion and patent to understand is Phrase-based indexing [webmasterworld.com]. Next to that (and possible BEFORE wrapping your barin around that] is hrase Based Multiple Indexing and Keyword Co-Occurrence [webmasterworld.com]
Note, this all started back in 2006, and by now it has become quite mature and advanced.