No one "accidentally" uses a corporate card for personal expenses. No one.
I generally agree with your post, however mistakes can and do happen. And I mean genuine mistakes. I have both personal and corporate AMEX cards. I once pulled out the wrong card and ended up using my personal card for a very expensive business dinner. It's not difficult to see why: both cards have the same general look and essentially identical graphics; the only differences are the presence of the company name under the cardholder name and the addition of "CORPORATE" on the background of the corporate card which is easy to miss, especially in low-lighting, since the font is the same color as the background and only has a thin black outline.
With all that said, I don't think that's what happened in Rubio's case. I don't know what to make of it really; it boggles the mind: he had serious political aspirations and was seen as a rising star in your party, so why would he risk even the
appearance of impropriety for a drop in the proverbial bucket?