The IRS has 'cracked down' on some companies for providing per diems in the US. IRS, of course, would like to tax per diem rates as income since they don't get any proof that the money was actually spent. Per diems for international travel are somewhat easier for companies to justify.
What makes the lack of a per diem a bit of a pain is when travelling to some countries where credit cards are not readily accepted. In a per diem situation, one can request an advance of the per diem based upon the expected length of the trip. Employees are thus spared the 'pain' of having to loan their company money.
Several years ago, when I was a 'non-exempt' employee, I successfully talked my boss into paying me for travel time. That happened for a grand total of 2 trips before it was decided that it would be cheaper to promote me to an exempt position!
Cheers,
'toad