You are sure to get some opposition here, but I'll give you my not-pissed-off points first and then you can deal with the roar you hear from others.
1) Personally I am not terribly impressed with the marathon distance. I've run 7 of them, and I did one after three months of training by running only one long run each weekend and NO other running during the week at all, and I still easily went way under 4 hours and I didn't even try at all in the race to go much faster.
2) Also, since I have run a 50 and a 40-miler up a mountain and back down, the marathon distance doesn't seem as imposing.
3) The training to run a FAST marathon isn't all that much different from training to run a FAST 10K. Just a little bit more mileage and a little bit more time during the build up, but that's it really. Want to run a fast 10K, and you need to be running 18 milers regularly. Want to run a fast marathon and you need to get that over 20 miles, but really it's not big deal.
4) I am way more concerned when I toe the line hoping to do a fast 5K than I am a marathon. In the marathon, you have so much time to figure things out, find a pace that is good. In a fast 5K, you need to make those decisions immediately or you'll be sucking wind.
5) Glad you like the marathon, and obviously you wanted to stir it up a bit, but I think most will agree with me here that ripping off those fast times in shorter distances is easily as hard if not harder than running a fast marathon.
6) Go run a 50-miler and then come back to me and tell me how hard a marathon is. A 50-miler over hilly trails is 10 times harder than a marathon any day, especially when you are trying to run it as fast as you can.