Hi Frank, resetting TCNT to 0 takes 250 nanoseconds on a 16Mhz Arduino. Because the timer is counting in 500 nanosecond ticks I don't think this delay makes any difference. Indeed I would be surprised to hear if any of the radio control equipment that would be used with this kind of application would notice differences in timing of less than a microsecond.
I am not clear if the ability to detect unlimited values for the pulse width are something one would would use in radio control or if you have another application for the code.
Many thanks for taking the time to share your comments, its always interesting to see the different ways people approach things.