Interesting post. I think a lot of modern motorcycles, especially those with the larger engine capacities are capable of big mileages but they're never allowed to reach their full potential for various reasons. I've never bought a high mileage bike myself but have had mates buy cheap used big bore bikes with over 100,000 k'ms on them and they've continued to run like clockwork with proper maintenance.
I agree, dunno about Oz yet but in the UK the average annual mileage is about 3000 for a bike. People get nervous about buying a bike with over 10,000 miles on it! I sold my FireBlade with something like 52,000 miles on it for £1100, no-one was interested especially when you could get one with less than half of that for £1500.
There is a guy in Melbourne that posted on a FireBlade forum, he has a '94 which he did 300,000kms on the first engine, and another 300,000 on the current one which is still going strong (and that was a race engine before he got it).
I think it's different running up high miles vs buying a bike that has already done it, but I guess if the price is right it might be worthwhile.