The first reason is because the data you send and receive from your devices is wrapped up in a different layer for sending across the broadband networks. This is typically 5% of your sync speed.
For example, a service based on the Openreach 40/10 FTTC service will give, in perfect conditions, a download speed of 38 Mbps and an upload speed of 9.5 Mbps.
It’s normal for the connection speed (sometimes called access or sync speed) to be different to the download speed (or throughput) that you see on your devices. This difference means it’s very important when buying Vodafone Broadband to understand that our Ultimate Speed Guarantee covers the sync (or connection) speed, and not the download speed on your devices.
While it’s possible to get great speeds over a Wi-Fi connection, the extra overheads of carrying your service over Wi-Fi generally mean that connecting with an ethernet cable will give a better result and speeds will be a lot less variable.