The condensation issue is a very good point and one of the biggest problems when it comes to storing a vehicle. Any semi-enclosed portion of the vehicle (diffs, trannys, engines, fuel tank, even the interior if the windows were rolled up) exposed to variations in climate/storage conditions runs the risk of forming condensation, and when the vehicle isn't driven, the fluids and cavaties never get warm enough to evaporate the collected moisture.
This isn't a large issue in more temperate climates, and less of an issue if the car is stored indoors, but it is still a problem. Another reason why it's important for a car in storage to be driven occasionally, because starting it and letting it warm up doesn't warm the rear end to drive off moisture. Seals can dry out and start to stick to things, and then when you go to drive the car the dry seals can tear because they're stuck to what they're sealing, which after months or even years of sitting stationary for some reason decides to start spinning.
As far as brake fluid goes-- it is Hygroscopic (read: it absorbs moisture). Brake systems are very vulnerable to sitting, and if they absorb enough moisture they can begin to rust.
Low mileage cars, as long as they are driven occasionally and have occasional fluid changes to get rid of any condensation are usually ok. My TTA has 2500 miles on it (I've had it for a month now) and I haven't had a single problem with it. The previous owner did start and drive the car occasionally, it was stored indoors in a semi-climate controlled shop, covered and out of the sun, and the oil was changed once a year. The tranny and diff were OK and free of any surface rust when I pulled the pans, and I flushed all the brake fluid and saw no signs of rust. I also flushed the gas tank and saw no signs of rust.
Some of these ultra-low mileage cars were purchased and just parked... original oil and all. No maintenance on a stored car isn't good for them. If fluids were occasionally changed and the car was at least started occasionally that's a plus, and if it was driven occasionally that's even better.
If it matters any, since I've owned the car (about a month now) I've put more miles on it in the last 2 weeks than the previous owner did over the last 5 years
I have had no storage related problems, but I made sure to throughly inspect all storage problem-prone items and do a complete fluid change when I bought it. So far, so good.