There's been a lengthy discussion of this in the comments, so let me make one last point about this. The last time Metro banned bikes all day was when the Pope visited. That was a busy day for Metro, so good policy, right? Except that since then, as of July 14th, we've had 8 busier days (and previously there were two busier days).
1 07-11-08 854,638 Baseball/Women of Faith Conference
2 06-09-04 850,636 Reagan State Funeral
3 06-25-08 846,388 Smithsonian Folklife Festival/Baseball
4 07-10-08 844,530 Baseball
5 07-08-08 835,072 Baseball/Basketball
6 07-02-08 834,956 Smithsonian Folklife Festival
7 04-03-07 831,508 Cherry Blossoms/Baseball
8 06-24-08 831,464 Baseball/Basketball
9 06-20-08 829,998 Baseball/Basketball
10 04-24-08 828,973 Baseball/Basketball
11 04-17-08 828,418 Pope Visit/Soccer
Does anyone remember the metro system being overwhelmed during off-peak hours due to bikes on any of those days? I don't. Can Metro point to any problems that came from allowing bikes on during off-peak hours on those days? I can't. So what was so special about the Pope visit? It wasn't even the busiest day ever at the time.
Now, I know, the Inauguration should crush this record and might top 1,000,000 and I'm all for a reasonable busy-day bike exclusion policy. But, considering that Metro was needlessly cautious back in April, you'll have to excuse me for not being willing to take their word for it when they say they have to exclude bikes system-wide all day long.
If they close a line or a station, they make a case as to why that piece of the system needs to be closed and for that long. If they can make a halfway compelling case as for why Metro needs to be closed to bikes system-wide from 4am to 2am then I'll shut up about it.