That's probably the reason why the majority of Harley riders keep their bikes for years (and why indians will as well) most of which ive seen at least over 120,000 miles but when you see the Japanese bikes they always break down. You can't even ride them. Sport touring bikes aren't so good in that regard for racking on the miles.
This is the biggest load of bullshit I've ever heard. Every Japanese bike I've had has been very reliable. If you maintain them, they are usually bulletproof. I put 16,000 miles on a 2008 Suzuki I bought new and had no trouble with it whatsoever. Wish the Ducati I replaced it with was as reliable but it wasn't. I just don't tend to keep bikes for more than 3 years or so and I tend to put 5-6k miles on per year. I bought my current bike last December and I have almost 6k miles on it currently (bought it new).
I know guys with 30k+ miles on Japanese bikes with no trouble. That isn't a lot of miles, I know, but once you start getting into 40-50k miles the bike loses a lot of its value primarily because it is so easy to find bikes with lower mileage for not a lot of money.
BTW-Sport touring bikes are fantastic for racking on the miles. They are very comfortable, have decent wind protection and they allow you to actually carry stuff easily and safely. To say they are not good for putting miles on is contrary to the design of a sport touring bike... it is just nonsense and I can't imagine anyone saying that who knows anything at all about motorcycles.
As far as what to look for. Look for damage, rash, broken plastics, fluid leaks, etc. Ask for maintenance records and do some research on what maintenance intervals are for the model you are considering. Make sure the bike starts up quickly and runs well. Start it cold and ride the bike, run it through all the gears, make sure it shifts smoothly. Check the chain for neglect, dry, rust, chain really loose, worn sprockets. If this is neglected, chances are the entire bike is neglected.
Sportbikes probably get the most abuse and are the most likely to be neglected because they are fairly inexpensive, younger guys buy them and finance them and just don't have the money to maintain them. Be very wary of a neglected bike. Even if the price is right, I wouldn't buy a sportbike with rash or signs of neglect. There are so many to choose from that I would recommend you walk away and find one that has been well cared for.
By the way, I asked a couple guys who tow bikes what kind of bikes they tow the most and with ZERO hesitation they both said Harleys.
I also wouldn't recommend a sportbike as a first bike for anyone. Learn on something smaller, lighter and less powerful. You will learn faster and become a better ride in a shorter amount of time.