I wouldn't have thought getting a yeast infection treatment over the counter would be that big of a deal, considering all the different treatments available off the shelf back in the US. What else do they think I'm going to use it for besides what its meant to be used for?
It's not so much what they think you will use it for, but what the law allows them to sell it for.
For example, if you want some 1% hydrocortisone cream to use on your arm, you can buy it from a pharmacy. However, if you want to use it on your face, the pharmacy is not legally allowed to sell it to you - it must be prescribed by a doctor instead (due to the fact that it can thin the skin and your face is more sensitive than your arm). The silly thing is though, that you can buy 1% hydrocortisone off the shelf in the US!
With the Canesten, if the licencing law on Canesten states that it can be sold for oral thrush, then that's fine, but if it states it can only be sold for vaginal thrush, then they are breaking licencing laws if they sell it to you for oral thrush instead.