The fact that with road riding.. you still have to putup with all the idiots of society... . You don't escape the jerks with cell-phones who can't drive. You throw yourself right into them, and hope you don't die.
With mtn biking, you ESCAPE these morons, and society. You can forget your corporate world job, and actually enjoy LIFE. You can sit on top of a ridge and look off thousands of feet as to what nature has created.. and just take it in.
Doing that with road? Hell no. Instead your sucking down bus exhaust, and being honked at by little Johhny Hotrod who thinks he's cool in his dumb Riced Out Honda.
Just my 2 cents.
-Matt