Also, productivity is nearly impossible to measure yet I'd argue that some of the "feel-good" benefits of work-at-home actually do result in higher productivity. Let's take a few:
1) Commute time: 2 hours that I can be more productive and/or take care of personal business that would have cut into work time 2) Focus: Everybody (not just execs) can have a door, can screen their interruptions, etc. This is vitally important for think-work and creative-work. 3) Other high-end perks that come for more or less free to the employer: healthy meals, exercise options nearby, potential 24x7 support when needed
Frankly, the only two arguments people are making against work-at-home boil down slacking and lack of face-to-face collaboration. Both are fixed by some technology and a measure of feedback and discipline.