The issue at hand is not censorship of unpopular speech, but one of restricting "popular" speech in order to ensure more relevance in the displayed search results, and their associated AdWords listings.
The use of the word "bling" is an example of a "popular" word that was once frowned upon by AdWords staffers as being an arcane slang word inappropriate for use in their listings.
While proponents of Google's policy point out that particularly in a global medium like the Internet, using proper grammar and punctuation enhances an individual's ability to communicate, critics, on the other hand, see the all-encompassing nature of the Internet as the perfect medium to express new forms of language, such as the increasing number of acronyms like "LOL" (Internet shorthand for "Laughs Out Loud") commonly in use today.
A recent New York Times article quoted Google's director for AdWords, David Fischer, as saying "We really focus on creating ads that at the most basic level have proper spelling and grammar so that they're clear to users. We really encourage clear, effective, to-the-point communication to searchers."
AdWords submissions are automatically pre-screened for unacceptable content and style guide violations such as multiple exclamation points, before being posted online, with the editorial staff manually reviewing listings for offensive material, and contacting advertisers with suggestions on how any problem areas may be remedied.
Google is not alone in policing their context-sensitive advertising content; Overture and other Pay Per Click (PPC) search engines also implement style guide driven policies to limit gratuitous advertising liberties such as upper case text and multiple exclamation points.
While submitted AdWords listings are compelled to comply with the style guide, search results, which are generated through website spidering and complex algorithms, are based upon the actual content listed on any particular page.