High mileage

Last night whilst running with my mate he said to me; you'll be running just over 100 miles before the weekend. I replied, yeah but my quality training is not suffering (same times) and my slow running is slow. However, I don't really know how well it could be if I did less miles. My higher weekly mileage is because it's not just training but due to another, useful reason; running gets me to work. The traffic from Wrexham to Chester is dreadful and as such the 10.3 miles takes only 15 mins more than getting the bus or car in rush hour. Also I think that running a lot slower on rest days for me is OK because my once at work I'm sat down for most of the day. Another advantage I find is that once I'm home in the evening I don't have to feel that I have to do exercise to keep fit. I've already done 20+ miles of running! In fact I don't run to keep fit, I run to 1) get to work; 2) To get faster / train for races. The result of those reasons is that I'm fit. I wonder sometimes if I would still run even if I knew is was damaging me some way.