Lane width does vary according to the volume of dancers on the floor. Good floor craft requires that a leader follow the couple in front of him (Provided that said leader is following the line of dance) without passing or changing lanes. What is so hard about that?
As for "tailgaters" once you have vacated your space it is no longer yours, it now belongs to the couple behind you. Tango is a progressive dance (along the line of dance). If you are having trouble with people behind you being in your way, you are going the wrong way.
If everyone on the floor followed these simple principals, floor craft would be easy. Just keep moving along the line of dance taking care to follow the couple in front of you (even turns can progress along the line if the leader has the proper skills). This is why some clubs will not allow corte's, they stop the progression of the dance. When it is very crowded it is the only way to move more than a few feet during a tanda (think about it, if one person stops, everyone stops).
Passing, changing lanes, and leading your follower into space that is behind you are three things that lead to most collisions during the milonga. If you are not part of the solution, you are part of the problem.
I would also add that if your dancing requires that you dance a sequence that you need to work on your improvisation skills (these skills are what made Tango what it is, a dance that can be changed in a fraction of a second).
I have visited areas where there is complete ignorance about floor craft, in these milongas it is often a free for all (Total chaos) this is the direct fault of "instructors" and shows everyone the skill level of those "instructors".
