I have no problem getting my WRX to slip into 1rst at 26-27 mph consistently. I am surprised that anyone would suggest that it is "normal" for a manual trans (of any make) to behave otherwise.
It is completely unacceptable for people to have to slow down to 5-10 mph or even come to a complete stop and shift into 2nd before being able to shift into 1rst.
I would suggest that anyone who has a WRX that behaves otherwise take it into their dealer before the warranty expires. This could even be a safety issue under certain circumstances.