Yes, I'm not disagreeing with this. However if you put ALL H1Bs in a single pool, and they go to the highest bidder across all industries, then yes, accounting firms are competing with tech firms.
I think GP's point is that that's the way it's supposed to be. The shortage of accountants could be due to some combination of:
1. There are not enough people with the physical / mental / psychological capability to be accountants in the US
2. People with the physical / mental / psychological capability to be accountants are choosing other jobs; perhaps because they pay better, or are more fun, or have better work/life balance, or whatever.
#1 is a reason to steal^W import capable people from other countries; but I doubt very much that's the source of accounting's problems. It's almost certainly #2. In which case, if accounting firms want more accountants, they should make the job more attractive: pay more, have better hours, etc.
Your company has to declare what industry segment they're in when submitting annual returns anyway (here), not sure if it's the same case in the US.
I think there would also be debate around how the quota is split between categories. I highly suspect that are much few Foreign Law advisors or Psychologists attempting to get H1Bs than there are "IT/Computer Professionals" (and many less positions available for them); giving each category an equal split wouldn't be fair either.
I'm not saying there isn't a way, but it would have issues too.