Two further notes -- I always book window seats, and would be "annoyed" to say the least if Amtrak were to move me to an aisle seat in order to accommodate the hypothetical NHV-PHL passenger in post # 1.

I have wondered why the online seat map does not get updated en route -- as people get off, leaving vacant seats, the online seat map should show that the seats are now available. But that doesn't happen. On my last NYP-WAS trip, my car was full when we left NYP, but only had about 10 passengers left when we left BWI. Yet, the online seat map still showed a full car!