Just send mail with any advice you have to the address at the bottom of the site. He may not agree with you, but he's more than reasonable about responding (everything in the inbox is read), and it will do more good (and probably get you more goodwill) than campaigning for policy changes in the middle of random threads.
It's also worth considering, when thinking about why it hasn't been banned, whether or not the main value from the threads (assuming the perfect source) would be from the link or the comments.
For some types of submission, it's the link: personal blog updates, academic papers, interesting technical achievements, detailed research, so on.
For others, it's the comments: company updates, interesting world news, most things happening in real-time, obituaries, so forth.
For others still, it's tied: blog posts on historical subjects, 'Show HN:' posts, submissions about different ways of doing things than mainstream methods.
Product launches, from my perspective, fall in the "Value in Comments" category. So then you have to decide whether it's worth the trade-off. By banning TechCrunch, would the site lose comment value?
Looking at this one, you'd really be missing some good comments by getting rid of TechCrunch links; there are all sorts of anecdotes about the product in this thread, and there are a bunch of interesting anecdotes about competing products as well.
