Google's offices wouldn't necessarily have as much bandwidth as their data centers. The real surprise here is that Google gives their offices massive connections (presumably to the GBone).
It's not that unlikely. Consider that the offices may have to push significant amounts of code/data back and forth between their offices and their data centers. You probably want to minimize the amount of developer time wasted.
Consider this question: Let us say the cost of an infrastructure at google HQ is X. X is the cost regardless of internet. Now let us say you have Y which is the price of an average inernet connection for google offices. Or you pay 4 * Y to get that connection. Ok lets make it 10 * Y. Whatever. The point is that if it makes your workers a bit more productive (5000 people?) lets say 3%. I think that 3% productivity on developers translates to WAY above the price of that connection.