He's right. The only reason outdoor records are faster is because:
Some runners feel that if they go hard during indoor season it may put them in a position to when they have to maintain their peak too long or if they do the 2 peak system they might not be able to be sharp in time for August
Indoor championships are only every other year so not many athletes want to go after records and get themselves in top shape early when they're not even going to be able to use that shape on the world championship stage
On the off years for outdoor (1 every for 4 years (no Olympics or WC like this year)) you still have the DL races which are going to still promote fast times (like Galen Rupp's 26:48 AR at the 2010 Brussles meet)
Yes, it is true that less curves are going to make it easier however, what about the banked curves? The fastest indoor track (in which most records are broken) have the same mondo surface that the fast outdoor tracks do so that's out of the question, but they also are banked. Banked track help with the centripetal force of your body when rotating around a curve and helps with your bodies torque (an objects ability to accelerate around a curve), are there any outdoor banked 400 tracks? No... So the fact that 400m tracks have less curves is an advantage over indoor tracks, but the fact that many fast indoor tracks are banked is an advantage over outdoor tracks. These advantages pretty much cancel each other out. Another factor is enviornment. In indoors you always have a controlled environment for optimal preformance while on outdoor you might have bad conditions. Therefore when it comes to environment problems, sometimes indoor tracks and facility can actually be faster.
You're more likely to get more money is outdoor races so because of financial opportunities this may be a upside for records outdoor being faster. In some countries, athletes don't get paid like US athletes, so when they have the opportunity to go to and try to break a record at a fast DL meet then they take it.
Indoor season is only from mid-Jan to mid-March, while outdoor season is from late march all the way to September if you include the last couple of DL meets so outdoor has a bigger time frame to set better times.
Also, to be aerobically fit, you must do a lot of base mileage from September-December. During those down months, it's going to be easier to peak long term (more towards the outdoor season) than to just do a bunch of base mileage and try to rip some fast times a month later, it doesn't work like that for most athletes.
Conclusion: Indoor tracks are just as fast, if not faster than outdoor track, but the shape of the athletes and the athletes wanting to do indoor is the reason outdoor records are faster.