@Setanta,
Not knowing the political stance or stature of this particular mayor, you make a good point about the limited ability politicians (and about everyone else) has in attending a certain amount of events in any given year.
That said, if his political base is in fact supported by a large number of gays and lesbians at the voting booth then perhaps a brief appearance is in order. If he then doesn't attend then he should be wary of the consequences come next election.
If not, then he should have the right to turn down any invitation because as you say only a limited amount of engagements can be attended any given year. Any backlash against such omission from an event would be pretty petty then.