they advertise the broad range because of multiple things. for one in California we only get 91, and you can get higher numbers on 93 and so forth. also, every GTI is different, and it's not like every single GTI that gets the flash is going to get exactly 44.2235 hp or whatever. throw in the fact that some people get flashed from stock, others get flashed when they are already modded, etc. and you can see that they have to advertise a broad range so that no one comes in expecting +50hp and then flips out when they get +40.
this all goes for every chip: in reality, APR should also be advertising a range of numbers instead of one single value. trust me, you are NEVER going to get a 20-30hp difference between chips unless something is extremely odd with the car. in some cases, I've seen people get higher numbers with GIAC, in others, people with higher numbers with APR, with Revo, etc. But even though people get different numbers, the key point is that the difference is MARGINAL in all cases. that's why I stress dealer location, features, etc. is more important than outright numbers.
also, if you want to know what people are getting with GIAC, search for yourself, no one is going to take the time to search for you. also check the 2.0 forums on vortex, they have a lot of member dynos.