Counter Argument
The counter argument to your main point is that:
1. More productive when they are in the field - e.g. paperwork can be done onsite rather than having to spend one day a week doing it
2. As such, that's another day that the sales rep or field engineer can spend on-site - out of the office - isntead of spending every friday in the office filling in spreadsheets.
People use to work remotely before, but it was pretty rare. Now it's near common place!
Of course you're right in saying that if there is/was a ligitimate business requirement for an employee to work in the field / at home then they would - regardless if it's 2007 or 1997. However the lines are a lot more blurred and there doesn't have to be a STRONG ligitmate business case anymore - people are now (or can be) just as productive on the road in 2007 as they were in 1997.
People aren't magically 'able' to work outside of the office anymore, but there's much less of a barrier so when an employee thinks it could be useful - there's very little downside - the technology enables them to be as productive.
Our client liason team used to spend about 60% at clients, and 40% doing whatever it is that they do in the office. Since we've deployed WM6 handsets to all with Exchange 2007 ActiveSync (and the added 3G data card) it's closer to 85% of their time is spent with clients - they only come in for meetings, rather than coming in for admin/paperwork.