It always amazes me when someone claims to know more than the tractor manufacturer...
I will bet if you check your manual it does tell you that a 50 hour service is required...
Why should the dealer care if you wait till 100 hours or do the service at 50 hours? Won't take any longer for his man in either case.
Remember, 50 clock hours could be 75 or 80 hours of seat time.
Now I will confess that I might have went a little over 50 hours on my BX before I did the 50 hours service, but that was because the BX hour meter is not tach driven and actually measures real time hours. Whereas the other tractor hour meter is tach driven and counts slower than real time, except when I run the tractor at 540 PTO RPM. Yet both call for 50-hour services.
Bottom line, if you are planning on keeping your tractor a long time, why risk it and skimp on the first service, when all the first service really is, is a couple oil and filter changes anyway.
No big deal...I would just do it and feel good about it.