Its not the geek factor talking. Ukemi on concrete is not an issue, breakfalls are. But we don't do it voluntarily.
You know when you do seminars, sometimes a hall is used with concrete floors and your mats are the interlocking ones? Ok, so the mat is crowded, your partner throws you right at the age, and you land halfway outside the mat. That's when you are most likely to experience breakfall on concrete.