I think this is different - to me, at least.
I bill clients for my travel time and mileage as well. The time it takes me to get to to/from the client's location is time that I can't do anything else. And the miles that I drive to get there and back are miles that wouldn't otherwise be put on my car. So, I capture them so that I get credit for the hours and money for the miles from my company, and my company bills that time and those miles to the client on which I was working.
And similar to what was said above, it sometimes depends on the relationship with the client. I'll always enter the time and miles, but in some cases, my company may decide (or be contractually obligated) not to pass those along to the client.
In my experience, that's how it is with professional services, and it seems reasonable to me. My available work hours 9and the work product than can come from them) are the product that my company's selling. Their goal is to bill for as many of those hours as they can. My goal is to make as many of those hours billable as I can. If I incur time for a client for travel to/from work at a client site, and my company doesn't bill for it, then it's the same as someone coming into a restaurant to eat, and then only paying for part of the meal.
I will say though, that if I drive straight from home to a client site, and then back home again, then I deduct out the time and miles from my house to my office and back, so that the client is only billed for the difference above my normal commute. If I leave from the office though, then there's no reducing, since it's all in excess of my commute at that point.
To me, it's way different than the airlines charging for carry-on bags, peanuts, drinks, and other stuff that has always been factored into the price of the airline ticket.