The 12V is not constant all the time.. It sometimes rises to 16V too..
Another option is a resistor and a pair of [u]protection diodes[/u] (the 2nd schematic on that page). I'd use a larger resistor (at least 10K) and you can leave out D2 if you're sure the input will never go negative.
Or, you can also use a voltage divider with one or two "protection diodes". (That's the same protection circuit with a 2nd resistor in parallel with D2.)
A voltage regulator is designed for power, not data. It's not fast enough for normal digital data and it could potentially load-down a data line. It's just the part for this application.