Yes, the pit signs are not a big deal. Once you learn that 80 km is ~48 km (in LFS, my conversion program is calling 80 kph = 49.7 mph) it is no big deal. But as I've said, having the correct units on the speedometer that you are use to is beneficial. If I was reading kph, I would be like "wow, I'm doing 150 and others are flying by me like I'm standing still!" It's the comparison to real life that allows me to say I've got a good speed at 150 mph rather than trying to think what the heck 150 kph is. 150 kph to me without calculating or having a conversion program seems like it is quite a fast speed when it's only 93 mph.
Sure, reading kph or mph does nothing as far as racing, but it is nice to compare what LFS feels like compared to what you would know in real life with the units you would know in real life.