Let's say, for argument's sake, that Daniel Komen has the world's best for 1.5 miles. His Two Mile/3k would have taken him through 1.5 at, lets say 5:55? Someone feel free to correct my math, or make the case that El Guerrouj could have finished another lap after his 4:44 2k and run 5:50. So the 1.5 mile for the best ever would probably have been around that 5:50 mark, maybe a touch under.
10 minutes, compared to 5:50 is 58% as fast. (350 seconds / 600 seconds)
World bench press record is either 722# "raw" or 1,102# with a bench shirt. That's an absurd difference, holy crap. But anyway, lets take that raw number. You can either plug in the discussion weight of 255 or take the 1.5x body weight (average weight of an American male is 194.7 per wikipedia, making 1.5x = 292#).
255 compared to 722 = 35%
292 compared to 722 = 40%
255 compared to 1102 = 23%, for comparison
So, in terms of how "close" to the World Record each of these are, it looks like running is harder. Significantly.
Think of it this way... compare that 1.5 mile to a 5k. What's the average finishing time for males in your local 5k? A thread on Letsrun (that I just accidentally closed and can't find again) posted that average male finish time is 28 minutes. That's 14ish minutes per 1.5 miles. Feel free to debate if these people can cut 4 minutes off their pace by dropping half the distance.
I think the Letsrun crowd is just naturally skewed towards thinking that running is easier than it is for normal dudes. Also, I'm SCIENCE! not MATH!, so feel free to call my out on my percents there.