Are you sure you represent the typical developer?

Possibly not (I have been involved in Open Source in the context of a business for over ten years now, so my experience is perhaps longer/deeper than some, particularly in the areas where business and Open Source bump into one another), but I rarely meet a developer that doesn't at least know the basic differences between the GPL and a "BSD-like" license. Knowing those two is actually most of what you need to know to develop with Open Source software without handing the legal stuff over to luck.

But, saying "the typical developer doesn't understand" software licenses is no excuse for not abiding by the terms of the license. That is the price you pay for admission to a wide world of awesome software that is enthusiastically free. You either pay the price and learn what the licenses of the software you want to use mean, or you simply can't use the licensed code. It's both an ethical issue and a legal one. I can't force anyone to hold to any particular ethical standards, but, the copyright holder can certainly make your life difficult if you don't follow the legal requirements.

I think folks who don't take licenses seriously don't understand how strong copyright law in the United States (and most of the developed world) really is. If someone comes after you with a provable claim of infringement, it could cost you a lot of money. I've been involved in a copyright suit, and the results were that the infringer ended up settling for $30k, even though no money was being made on the copyrighted work (I was giving it away for free, and so there were no losses on my part; but copyright law allows for multiple layers of penalties and had it gone to trial it would have cost them at least that much).

If he did a google search for a code snippet to perform a task, and ended up on SourceForge, would he read the license or would he simply drop the code into his project and get on with his day?

Sure, people violate copyright all the time. People also pirate software all the time. It doesn't make it OK, and sometimes folks get caught doing it and it costs them or their employer a lot of money, time, or both.

I think hanging out on sites like HackerNews, filled with some of the smartest programmers around, clouds our perception of the "typical programmer".

Open Source programmers tend to be towards the smarter, and more importantly better informed, end of the scale. That doesn't account for the problem you mention of proprietary programmers "borrowing" liberally from Open Source projects without abiding by the license. But, when those things happen and they are exposed, there's usually a shitstorm over on Slashdot and the company in question gets harangued and ranted about and blogged about and occasionally sued until they comply with the license (either by rewriting the offending code and making a monetary contribution to the FSF of EFF, by way of apology, or by giving back their changes and using the software according to the license). One such case was discussed here on HN just a couple of weeks ago.

It happens all the time, and only a small percentage of people who use Open Source software without abiding by the license are ever caught. But, I'd like to think that things are getting better as awareness of Open Source increases.