You're not wrong, exactly, just a few years out of date. Here's the way it goes in 2011:

1. There is a constitutional difference between an "administrative" search and a "criminal" search. Except that Congress said to TSA "make sure 9/11 doesn't happen again, we don't care how" and walked away. Also, the Constitution is apparently DOA.

2. The government may do an administrative search for the purpose of ensuring that no weapons, explosives, or incendiaries get onto a plane. An administrative search does NOT need a warrant or probable cause. They may not use an administrative search as an excuse to look for evidence of a a crime. Except that the TSA needs to keep assuring Congress and the public that they're doing something useful. And the only successes TSA has achieved (or is statistically likely to achieve) are finding drugs, fake ids, people with outstanding warrants and illegal immigrants. So searching for evidence of a crime is necessary.

3. A criminal search is for the purpose of obtaining criminal evidence. Only a LEO can do a criminal search, and only under specified conditions (suspicion of crime, with a proper warrant or probable cause.) See above. They can't let that pesky Constitution get in the way of finding fodder for PV.

4. If the government conducts a legitimate administrative search. and happens to find criminal evidence/contraband, they have to employ a LEO to seize it. Depends on what you mean by "seize". TSA Joe is standing on the other side of the x-ray belt holding your backpack in one hand and a baggie of drugs in the other; he's not about to hand it back to you. But yeah, they have to find a real LEO to come arrest you and take the evidence to the police station. And it appears that in many airports, the local LEO is happy to oblige. Why wouldn't they be? They get credit for the arrest without having to do all that tiresome investigation.

Seriously, you're right but nobody, from Congress and POTUS down, cares.