I am quite shocked at what I’m reading on this thread concerning the criteria that some folks think is acceptable procedure in determining whether or not a spray is required. As I said in an earlier post the tail plane must be inspected and a walk around just doesn’t cut it. How do you know what’s on your tail plane unless you are in a position to actually inspect it? Do you jump up and down trying to observe your tail plane or do you just assume a clean wing indicates a clean tail plane. A contaminated tail plane is going to cause you to crash just as easily as a contaminated wing. If your tail plane is not getting inspected you're rolling the dice.
I have certainly witnessed carriers that were rumored to be in financial straits forgoing the de-icing spray while everyone else was getting sprayed. For someone to say that financial considerations are not playing a part in some de-icing decisions is pure folly.
IMHO there certainly appears to be a wide gap in the operational philosophy between what the legacy carriers and LCC’s are putting in their manuals. The legacy carriers build the proper method of de-icing into their infrastructure and follow through. Others prefer to go the cheap way and rely only on input from one source after a cursory inspection.
As others have wisely noted if you think de-icing is expensive, try an accident..