This is an interesting question. I think one answer is that we often notice unpleasant things more than pleasant; and often take the latter for granted - therefore words were more likely to be coined for the former group than for the latter. Moreover, naturally occurring "unpleasant" smells - eg those associated with excreta and decay - seem generally to be stronger and more intrusive than naturally occurring "pleasant" smells, such as those of flowers and spices. (Incidentally, I have put quotation marks round "pleasant" and "unpleasant" because it is only evolutionary programming that causes us to categorise smells in this subjective way. This progamming is very evident with some foods - eg strong cheeses - which smell pleasant to those who like them, and most unpleasant to those who don't!)
'Perfume' is, of course, also a verb, as is 'scent'..."The roses perfumed/scented the air beautifully." In addition, though rare, the following words also exist: 'cense' and 'thurify', from the censer or thurible used in Catholic churches to waft sweet-smelling incense. There is even an 'aromatise'. So, there are five suitable verbs to be going on with!
It's ok, xyzzy - Don't be too hard on the rev - according to the Oxford Dictionary all the words he used are indeed nouns - but perfume and scent are 'action verbs' used in a proper context - so says Roget's Thesaurus of English Words and Phrases.
sorry, revCrowley, i woke up feeling grumpy. Maybe I should have phrased my question thusly; Qualifying nice smell verb should end in 's' and be accompanied by 'it' as in 'it stinks in here'. Maybe I should invent a suitable verb. I bet the French got loads...
Just in case anyone imagines I have started copying others' highly-rated answers, I must point out that my earlier answer - including both words and an illustration of the grammatical point - appeared before Cetti's 3-starred response. It is below Cetti's now only because star-rating an answer pushes it up the page. Good luck to you, though, Cetti!