I've owned all of these dildos over the years (blushing, lol), and the manufacturers have definitely enlarged some, if not all of them, from their real sizes.
The Julian and Shane Diesel ones are enormous. I can't even get my mouth around them and I've seen both of these guys get head plenty of times from women much smaller than me.
Shane Diesel has some videos of him playing with a replica of his cock, but I don't think that's the same model being sold commercially. For one, it's darker, and also it appears to be a bit smaller as well.
Rocco also did some videos with his dildo, but I think the one they use on film is a life size model, as opposed to the ones sold in the stores.
I read somewhere that Falcon enlarges their dildos by about 30% from actual size. I think many of these straight porn star dildos do the same, they try and get them all to be around 9", when in reality they are probably about 7" if that.