saffer
Any US visa which isn't a green card (e.g. tourist visas, student visas) is considered a non-immigrant visa. You can only apply for, and enter on a non-immigrant visa if you don't have immigrant intent. If an international student, for example, applies for a green card, this shows immigrant intent and they could find it difficult to renew their student visa or even to re-enter the US after traveling.
Obviously this wouldn't be a problem if the green card itself were quickly approved, but the process is bureaucratic and can take years even for people with advanced degrees.
H1-B visas, on the other hand are one of the few visa classes that allow "dual intent", meaning that while they're non-immigrant visas, H1-B holders are also allowed immigrant intent. Which makes it a good visa to have before starting the green card process, if you want to be able to travel (e.g. to visit family) while your application is pending.
Also, as a potential future immigrant (native English speaker, doing a PhD in the US, not very culturally distant from Americans except perhaps for a greater appreciation of Monty Python) I would feel extremely alienated if told I had to pay higher taxes for the rest of my life just because I was born elsewhere. The current immigration system may be frustrating at times, but at least I can hold onto the hope that if I become a citizen here, I will have the same rights as everyone else. (Except running for president, which isn't relevant to my planned career path anyway.)
I know people with math, statistics and aeronautical engineering backgrounds who've worked at Google and Microsoft. I'm sure physicists would fit in too.
Otherwise I'd be asking my employer how difficult it is to transfer to their Canadian office...
As an English speaking South-African finishing a PhD at an American university, it's good to know there are other options if the U.S. decides not to give me an H1-B (the quota was exceeded in the first week, so apparently we all get put through a lottery: https://news.ycombinator.com/item?id=5513761)