In all honesty, I would only switch if it's giving you real mechanical problems with your picking technique. I wouldn't do it just for the sake of being "normal". ;) J/K

No seriously though...
There are a lot of really good players that hold the pick with the thumb/index/middle finger combo. Steve Morse (one of the most prolific alternate pickers EVER), Eddie Van Halen (at times), James Hetfield, Doc & Dallas Coyle (God Forbid), Glen Drover...I'm sure that there are many, many more that I'm not thinking of off the top of my head. But suffice it to say, that holding the pick like this can work for you, so don't feel that you HAVE TO change, just because most players don't hold it exactly like that.
If you really feel that it's holding you back somewhat, then that's a slightly different story.

Hope that's somewhat helpful. :)

Don