Yesterday in a Google Webmaster Hangout with Google's John Mueller I asked John if Google crawls penalized sites less frequently and/or slower. He responded that Google typically does not slow the crawl for penalized sites.
The reason I asked was because sites that get hit by an algorithmic penalty need to wait for Google to crawl the site to pick up on any changes and then for the algorithm to run. Meaning, if you get hit, you need to make changes to your site, then you need Google to crawl and pick up on those changes, then you need Google to rerun the algorithm. If all is good, you are removed from the algorithmic penalty.
If penalized sites get crawled less often, then that process can slow down even more. Why would Google crawl penalized sites less often? I'd think that sites hit by algorithms are deemed less important and thus Google may not want to use their crawl efforts on those sites. But John says no, it doesn't exactly work that way.
You can watch my question and John's response 22 minutes and 40 seconds into the hangout.
Forum discussion at Google+.