It seems to be missing a very big factor: culture. If your goal is to implement some code for, say, healthcare, it is a lot easier to explain the business process to someone who is already familiar with how stuff is done on a higher level. Whenever you hire someone from a different culture / country, you need to start from the basics by explaining the very core of your society. An American programmer might not be too…
There are a number of technology-specific hubs around the world and even just in the united states. Silicon Valley is one of the most obvious ones, but Raleigh is another one, as are Nashua, Boston and Salt Lake City (there are others).
What all of these have in common is that each of them had, at some time in the past there was a massive company with out-sized returns. In the Valley were were _several_ - Intel, HP, ... and many more. NCR (and others) in Raleigh, Westford, Petaluma (optics), Boston as a geography absolutely dominated storage until Netapp, and so on.
When you have companies like this, they produce a lasting geographic concentration of talent, especially early in a given sector's life. Think Michigan and especially Detroit for automakers or California for aerospace.
The experiment we're doing with the work-from-home thing will be interesting if it goes forward, because as a few locations in Canada demonstrated, a very active de-centralization of a given kind of expertise (in that case, the network element management software) can render a given tech hub a memory at best. If history is anything to go by, disassembling Silicon Valley, if possible, will not result in more uniform distribution, it will just move from one concentrated area to another.