love that video! I knew the 7D was tough, just not that tough. personally I don't plan on drowning, freezing and setting mine on fire any time soon - but you're right, it can take some serious rain without much worry. living in vancouver this is a prerequisite if you want to shoot year round. so far I have had no issues, and I certainly don't hesitate to use it in less than ideal conditions. I don't doubt that the 1 series have better weather sealing (as they're designed) but the 7D appears to be tough enough for this amateur on the wet coast.
If you are mostly shooting outdoors, have you considered the EFS 15-85? I find it a very handy and high IQ lens and would fill your gap quite nicely. It can be had used for around $550-600.
I have - nearly bought it in fact, but I shoot in so many low light situations, and use 2.8 on both my other lenses often enough that I figured I need the speed. it's a great lens for IQ but looses on both the speed and build. to bad - because you're right, it fits the gap better than anything else (with the exception perhaps of the 24-105).