Attempting to stop people or bombs in under carriage would EXACTLY BE SECURITY THEATER. That is an overreaction to insignificant but recently hyped/fear mongered threat that results in no statistically significant reduction in risk. But, writes up good in the papers.
People thinking like you are why security theater can exist.
However, I wasn't saying that we should be trying to stop this. I meant to show up, conversely, that a lot of the existing security is there merely for show.
How many planes have been bombed by someone sneaking something into the wheel well?
I can't imagine it would be too hard to place a bomb in the wheel well of a plane parked in Nairobi, for example. The biggest issue would be avoiding the pilot's pre-flight check.
That wouldn't be to hard to do if you are a member of a ground crew that has access to the aircraft after the pilot is on board.
BTW, we keep bombs out of the cargo area well because there was a time we didn't do this well at all. Then this happened: http://en.wikipedia.org/wiki/Air_India_Flight_182 along with this: http://en.wikipedia.org/wiki/Pan_Am_Flight_103