The difference is that at least donations are (supposed to be?) listed and tracable, and can be scrutinized if necessary.

Compare it with the sort of corruptino you find in countries like india, and china, where you _have_ to give money to the official to get your paper signed to do somethign that ordinarily you should'nt have to (e.g., may be you'd like to open a car import/export business. you'd be paying quite a few visites to gov't officials with expensive gifts or unmarked bills).

Takes a little bit of epistemology to make sure that what you think you perceive is in fact what is really going on (how do I know what I know?). Corruption may be going on all around people, but they see it as "business as usual" or it's built into the "lawful" system, so isn't perceived as corrupt (though it is visible).

Some people expect a certain amount of "low-level" (harmless?) corruption, so reserve their identification of corruption to particular visible or impactful events.