Although the judge's decision sounds absurd at first glance, I support it, even though I bet most cops can tell what marijuana smells like. The problem with allowing "smell searches" is that, smell being subjective (and often short-lived), a cop could search any house he wanted merely by saying he thought he smelled marijuana, and there would be no way to refute it either at that time or in court.
Once a cop has legally entered on probable cause, he would be free to note any other illegal objects or acts; the absence of found marijuana (which "might have been fully consumed or flushed down the toilet"), would not hinder prosecution on other charges. So if the judge decided otherwise, the 4th Amendment would become virtually meaningless.
The practice of no-knock raids has already rendered the 4th Ammendment virtually meaningless. What freedom we enjoy in this country, or what freedom we think we enjoy, is overly dependent upon the benevolence of our police forces, and not so much upon the rule of law as it should be.
This is a good ruling, and I support it too (like you).