My understanding of H1B visas is that they are sponsored and that if you leave the sponsored job, you have to go back to wherever you came from. That's what makes it so attractive for employers.
H-1B Visas are attractive for employers because they are the easiest way to bring in foreign workers, especially from China and India.
The Employment Based (EB) Visas are limited to 140,000 per year, but more importantly they are limited to 9,800 per country.
For example, the Visa Bulletin says that for China, they are now working on EB-2 & EB-3 Visa applications from 2011, and for India they are now working on EB-2 applications from 2007 and EB-3 applications from 2004. Hey, what's a 10 year wait?
In FY 2012, 136,890 H-1Bs were issued for initial employment and 125,679 were issued for continued employment.