This is a complicated issue. If you read forums, there are a few folks complaining about any and every laptop on the market. Why? There are so many wireless routers out there running different protocols (a,b,g,n, ac) on different channels and bands with a vast array of firmware and brands. 100% compatibility isn't going to happen. Especially with old router firmware.
And some models do have weaker WiFi, like the Sony Vaio Pro 13 and Duo 13 don't have very strong WiFi. Should you buy a laptop and love it but find you're having problems with WIFi, try changing router bands and updating firmware on the router. Also make sure the laptop has the latest drivers. These can really help. And if you like everything but WiFi on the laptop, USB WiFi adapters are a cheap fix (if you don't want to ditch the laptop).