Those are best-case scenarios. In reality, the Acela takes 8 hours to get from Boston to Washington, DC -- a flight I've made in about an hour and fifteen minutes.

I take Acela weekly between New York and Boston. While the flight is only 1 hour and 20 minutes, it is much slower overall.

Acela

4:52 leave work, walk across the street to Penn Station
5:00 take Acela from NYP to BBY (work on train for a FULL 3 hours)
8:30 arrive in BBY
8:40 take a cab home
----
3:48 Total Time (all public transportation) -- FIXED TIME!

Plane

3:15 leave work, take cab/subway to LGA
4:00/4:15 arrive at LGA
5:00 deal with check-in security, luggage concerns, board plane
6:20 arrive in BOS (work on plane for a max of 45 minutes)
6:30 unboard plane
6:40 get out of airport, get cab
7:05 arrive home
----
3:50 total time

While the times are similar, the train is 3:48 EVERY time. When I took Delta shuttle it varied from a minimum of about 3:40 to a maximum of 9 HOURS -- exhausting after a full day of work, with an average of about 5:15.