got an answer from C-Span's Capitol Questions concerning this vote and House rules...
My question:
Two nights ago, the House voted in favor of suspending the rules and passing a bill. It was a voice vote, and there were only about 20 Congressmen present on the floor at the time. (The bill was H.R. 4210.) How can a bill be allowed to pass when so few Representatives are present? What are the rules concerning a quorum being required? If the motion to reconsider is immediately tabled, does that mean that the vote is final even though only 20 members were present?
C-Span's answer:
Suspension of the rules takes a 2/3 vote to pass, whether it's by roll-call [a certain discernible number] or by voice vote [judgment of the chair that 2/3 said "aye."]
Members may choose to pass anything by voice vote. They have several procedures to call upon if they wish to get a roll call vote.
Only roll call votes prove the absence of a quorum. If the absence of a quorum [218 in the House; 51 in the Senate] is established, the vote would be invalid.
Although the written rules of the House and the Senate both require that a quorum be present at all times for business to take place, the reality is that it rarely is except for roll-call votes.
This practice is known as a "presumed quorum." In other words, a quorum is presumed to be present unless it is pointed out that it is not. That would be done by either a point of order that no quorum is present or by the numerical evidence of a roll call vote not adding up to a quorum.
Members can easily make a point of order -- and do, often -- that no quorum is present. Then business is suspended until a quorum materializes. But the quorum requirement must be enforced from the floor -- individual Members must feel strongly enough about it to make the point of order. Otherwise the presumed quorum continues.
As for the motion to reconsider, yes, if it is tabled the vote is final and cannot be reopened for lack of a quorum or for any other reason. See:
http://www.c-span.org/questions/weekly85.htm Best Wishes, Ilona Nickels
C-SPAN Resident Congressional Scholar
So, a bill can be passed no matter how many (or how few) Representatives are present on the floor at the time. As long as nobody present objects to the lack of quorum, and as long as there's no recorded vote proving the lack of a quorum, the vote is final.