Why is Google indexing parked domains? Money. What information on a parked domain needs to be organized for general search? None or almost none. All this does is add an extra paying click between the user and the information they are after. It builds millions of indexable billboards into the index so people will pay for traffic that they could get straight from the SERPs if the parked domains weren't there.
http://www.webmasterworld.com/forum89/11369-5-10.htm The problem is that Google owns oingo.com, one of the largest "parked domain" companies out there and not only indexes them in their database but also serves advertising on them and integrates these sites with the database of the normal sites. the fraud is
Yahoo! and Google are breaking this “Pay Per Click Promise” by allowing these ads to be placed on pages other than search results. This type of Syndication Fraud is running rampant across the web particularly among parked pages (where domain speculators purchase domain names for the sole purpose of monetizing the natural traffic on them) and dynamic doorway pages (dynamically generated pages are created to fool search engines so they can show up on natural/organic search results).
http://www.threadwatch.org/node/6110 Some advertisers complained about this and got this response from Google when they didn't want to accept the fact that even the site exclusion tool for their adcampaigns didn't allow them to opt out from such domainparking (fraud) services. I understand that you're concerned that your ads may be appearing on Google-owned-parking service.com even though you've added this URL to the site exclusion tool.
Google-owned-parking service.com is part of the Adsense for Domains networks and although most of these sites may be excluded with the site exclusion tool there are some exceptions that may not. This is due to the fact that some of these sites are of a hybrid type and are considered both part of the search and the content network. Oingo is one of these exceptions. To learn about the difference between the search and the content network please visit https://adwords.google.com/support/bin/answer.py?answer=6119&hl=en. To effectively filter your ads from this site you may want to consider opting certain campaigns out of the search network. If you opt out of the search network, your ad will no longer appear on your unwanted site, nor will it appear on any other site in the search network. However, opting out of the search network may significantly reduce your ad coverage and visibility to prospects.
http://www.threadwatch.org/node/6110#comment-37313 translated : If you opt out our domainparking service, than your visibility across the whole database will suffer. Blackmail. The other problem is that by owning Oingo Google owns now domainnames with tradenames from her direct competitor and off which these domainnames have as sole purpose to redirect traffic from this sole competitor (source Microsoft research) Domain: google.com
It is also a problem that Google serves advertising on these kind of pages, which would be the same as placing ads on stolen cars.

http://www.wiredsafety.org/law/copyrights/typosquatting/index.html what is typosquatting July 8, 2005SAN FRANCISCO - An Internet arbitrator has awarded Google Inc. the rights to several Web site addresses that relied on typographical errors to exploit the online search engine's popularity so computer viruses and other malicious software could be unleashed on unsuspecting visitors.