The speed they will be referring to is the speed you get when connected to the router with an ethernet cable.
Any provider who lets you leave because you have rubbish WiFi speeds is not going to be around very long.
WiFi is such a pain in the rear end, I only use it for my tablet and phone, and thats only because they dont have ethernet ports.
Anything that has an ethernet port has a cable in the thing. Its the best way to make sure you're getting the speeds you are capable of.
I will say though, my Home Hub 4 on the 5Ghz connection to my Galaxy S4 does give me the full (give or take a mb or two) the exact same speed as my ethernet connected PC.