Afaik 2 machines are almost mandatory
1. Dev machine
2. Email machine
The 2 biggest orgs inside MS are Office and Windows, devs in both of them can't have a single machine doing both the above tasks. (And VMs suck for disk based I/O, and that becomes a factor when you have multi-hour build time)
Yes, economy does impact internally at Microsoft. Thankfully, we have Hyper-V to have more than one OS in a given box. But back in the old days, two machines per person was pretty standard. I no longer work for MSFT, so not all orgs still stick to the same policy