Are there any drivetrain components designed and sold to last longer?
This doesn't help with the longevity of parts, but if you are doing 100 miles per week, you may want to learn to work on the bike yourself, and invest in your own tools.  Let's face it, at 100 miles per week, you'll probably be working on the bike at least a couple times a month (bearings, brake adjustments, flat repairs, etc).  So why not add in the tools to do your own drive train, and lower the cost down to parts alone?

For your drive train, you would need a good set of hex wrenches ($19.95), a chain breaker ($15.95), a cassette tool ($5.99), a chain whip ($21.95), and a crank puller ($13.95).  After tax, this would come out to ~$78 (according to JensonUSA.com), but would give you everything except parts you need to do the work.  I have a hard time imagining that this wouldn't pay for itself within the first year of regular maintenance.

I would also invest in a chain cleaner, as they can increase chain life depending on your usage.