If you have 1 kill and NO deaths, you end up with a k/d of 1/0, which really annoys most programmic math APIs. K/D+1 ensures you have a legal operation.
Of course, it makes your K/D calculation WRONG, but it is easy.
Personally I think there needs to be two scores; streak and K/D. When you have no deaths k/d is worthless, and if ($DEATH=0) {ignore}. Once you have died, then you can worry about K/D ratio. Streak is simply the number of kills since your last death/capture. A bail/landing wouldn't count against streak or k/d.
Just imagine, in WWII, George Preddy gets his first kill, but can't put the flag on his bird because his k/(d+1) is still 1...and after his first death, rather than a 1:1 k/d he's at 1:2 for some reason...
Anyway, put on your nomex underwear, because the score potato flames are about to start...
Just my 2 perks.