[Proj] differents results between cs2cs and proj

[Lionel Barth]

Hello,

I am a new proj user.
I do not understand why I have differents results using the following 
proj and cs2cs scripts :

The script :
"proj    +proj=lcc +lat_1=45.8989 +lat_2=47.6960 +lat_0=46.8000 
+lon_0=2.33722917 \
      +a=6378249.2 +b=6356515 +x_0=600000 +y_0=2200000 \
      4.34878E 44.35930755N"
 answers "760474.90       1930742.15"

while the script :
"cs2cs    +proj=latlong +datum=WGS84 +ellps=GRS80 \
  +to    +proj=lcc +lat_1=45.8989 +lat_2=47.6960 +lat_0=46.8000 
+lon_0=2.33722917 \
      +a=6378249.2 +b=6356515 +x_0=600000 +y_0=2200000 \
      4.34878E 44.35930755N"
answers "760465.95       1931091.70 58.36"

The differences are 9 meters and about 350 meters. Does anybody know why ?

Thank you,
L. Barth