I guess the reason BF2player doesn't count them in the ratio is they won't count towards any awards (have to be direct kills for any awards with IAR req). Still i think its a bit silly to not count them in the ratio as the road kill never would have happened if you weren't in the vehicle in the first place...
Roadkills count as "kills" they just are lucky enough to get their own category. On a side note it does seem the roadkills needed for transport badges need you to actually run people over, for me personally anyway...