bumpski - 2:12 pm on Jan 13, 2013 (gmt 0)
There's the other side of the coin.
Some bots are causing false ad impressions. This is theft of services. One would think a webmaster should do all in their power to prevent false ad impressions and thereby "legally" justifying providing different results to bots than they do to legitimate users of the site.
Google's preview, for instance, generates ad impressions, corrupting impression counts, etc. Sure its not much, but still the advertisers are paying for these impressions! (At least for pay for impression ads.)
Unfortunately Google has their own perspective (on the world) and Yes it probably is dangerous to hide ads! So it's the Scorn of Google, or, Theft of Services? As I said; the other side of the coin!
Oh by the way Google's preview, and probably other preview bots, use a fixed width format, which of course very few "legitimate" users would be using.