I only ever have Tikka as it is intended, i.e. served on a sizzler with a bed of onions (unless i'm at home of course). I must say though I haven't seen many that offer Tikka in curry dishes. Mind you, I rarely shop around for my curries when eating out, choosing to stick with what I know and like so that might explain it.
The questions should be, is there any real noticeable difference in this variation. Surely the flavour or a peice of tikka would be lost in a dish like a vindaloo. Would someone really be able to taste the difference between a Chicken Vindaloo and a Chicken Tikka Vindaloo?
I guess there must be something in it as it is clearly on menu's as an option but too me it just seems over the top.