Hi, I'm looking at getting the Asus G751JY but am a little put off by the issues.

I have a few questions;
1. Does anyone know what the difference between these models are? I can't see any difference in specs I found with retailers. I'm hoping its an updated version.
2. The WiFi issue that some are reporting can be fixed by just adding a mini wifi USB adapter right? How widespread is this issue? Is it specific models or a flaw in the design that affects all models?
3. I can't seem to find a battery replacement service? If it come to it and the battery capacity dropped considerably in say 2 years time I'd like to know there is the option to have it replaced and it's not too expensive...

Thanks to anyone who can answer any of these questions, I did do a search on my main question about the model differences and couldn't find anything.