It can be trivially amended without change in salary - you don't even need to wait for the amendment to be approved before you can move the employee to the new location. In any case the point still stands that there would need to be location specific minimum salary requirement.

Not legally they can't. I changed location from South Bay to San Francisco within the same company (a move easily within commuting distance) and they had to file a new LCA and an amended H1-B.

So? Did you have to wait until it was approved? Not sure what you're disagreeing to here.

Well in my case it was approved in 15 days via premium processing, months before I started working.

But in general you're correct that employees can change work sites while the H1-B petition is pending (because without premium processing that takes months), but only after the new LCA is approved. And the LCA is what determines the prevailing wage for the new site. So you can't move someone from Bumfuck, Nebraska to San Francisco and continue paying Bumfuck wages.

If you think the processing time is too long - I totally agree. 15 days should be regular processing time, not "premium".

Right, and these H1B shops are getting by that by telecommuting. It's exactly why Disney was able to find immigrant IT workers who could do the same job for less.