FTC has cleared Google - AdMob deal

I am by no means an authority on this subject but does the whole concept of a 'monopoly' (or such) on advertising not strike anyone else as as bit... silly? As in, to advertise one only needs some sort of property and then no one could stop you using it to host advertisements.

I suppose you could say the same about any industry - if you own property then you can attempt to enter the market. But something strikes me as different about advertising, can't quite put my finger on it.