In traditional SEO battles, this may have been true. Cloaking, paid links, scraping, keyword stuffing; Google fought these and largely saw their best interests served.
Now, Google is in shaky territory, where winning the battle may cost them the war. This is the trouble with expanding into other markets and against new competitors; the old rules just don’t apply.
The Incentive for Google+ to Allow Spamming and Abuse
Google+ is Google’s latest major attempt to launch into a new market. The biggest problem they face is that, as with any Google property with marketing potential, marketers looking to use/abuse the system are often faster than Google itself at finding loopholes.