http://www.champcars.../recordbook.htm
For being that American open wheel racing spent many years running only on ovals (a couple of road races a year on occasion) for the first 80ish years, you had many greats not do that well on the road circuits. Of Foyt's 67 wins, only 3 came on road circuits.
Even more modern, Hornish scored 19 IndyCar wins (on 116 starts). None on a road circuit. Of those starts on road/street circuits (11), he scored 2 top 5's (2nd @ Watkins Glen being his only podium).
In all honesty, I think Marco Andretti is starting to fall into this group. He is one of the fastest on every oval. Hasn't scored many wins (1 in 2011), and does have a road circuit win, but his name is always talked about much more when the series is at an oval.
Trying to not go beyond the introduction of CART in '79, and finding it hard. You had the guys who where some of the top drivers in the IRL to struggle after the merger (Buddy Lazier, Buddy Rice), but they were not with any winning teams at the time of said merger.