Internet connection speed is a made up by a combination of bandwidth and latency. That's the reason why large organisations will spread servers all across the country/world. By limiting the number of hops they can guarantee that the data gets to you quicker with fewer data collisions along the way (that require some packets to be re-sent).
In the realm of home networking think about Ethernet vs Wireless. In ethernet the signals are already converted to the format used by 802.3 networks when they come through the gateway. To send them down the line they are buffered and piped through to their specified destination with little or no signal or packet loss due to the direct wired connection and simple infrastructure.
With wireless 802.11 the signal needs to be converted to the correct format by attaching wireless specific info to the packet, then the packet needs to be converted to a wireless format that can be transferred. Factor in wireless interference and the fact that a lot of packets will be corrupted along the way due to the frail nature of radio transmissions and the high factor of interference; and you have a lot of packets that'll need to be re-transmitted.
All of those factors add increase the latency of the data transfer. Even though the distances of travel are trivial, the additional complexities that make wireless 'work' will inevitably increase the latency.
If you had top-of-the-line equipment and you lived in a radio vacuum you may be able to get WiFi latency that comes close to ethernet but... In a realistic environment, a little occasional lag is the best you can hope for.
There are certain settings you can tweak on a wireless to attempt to improve the connection quality but, with everybody running personal wireless routers in close proximity, there's bound to be a lot of interference.