Gigabit transceivers datasheet with errors?

[F_Handy]

http://learn.extremenetworks.com/rs/extreme/images/Pluggable-Transceivers-DS.pdf contains on page 3 the information that the MGBIC-LC03 supports 2 km with OM1 cable while at the same time the device supports ONLY 1 km with a better fiber cable of type OM4.
Can you elaborate this scenario "better cable but less distance"?

[Drew_C]

I packed up Randy's answer and put it into GTAC Knowledge for reference in the future:
Why does the MGBIC-LC03 datasheet state 2 km distance with OM1 fiber and only 1 km with "better" OM4...

[Ottman__Randy]

Correction of an error in my response above - all references to "1000BASE-LR" should of course be "1000BASE-LX" - apologies for any confusion.

[F_Handy]

Randy,
I'm really impressed by the speed and quality of your answer!
Thanks a lot!!!
My question has been answered.

[Drew_C]

Thanks. I went ahead and edited your post to show this correction.