Yeah, WiFi is dependent on your home internet connection speed, which will always be lower than advertised (i.e. "$50 for 25Mbps Broadband" will NEVER hit 25Mbps) due to overhead, "sharing" with neighbors, encryption, and distance from hub. If you're paying for 25Mbps, you should expect anywhere from 5-15Mbps; also, WiFi is ALWAYS slower than wired connections, it's a fact and there is no way around it. Adding the additional encryption of WiFi as well as the variations in signal strength, distance variations, and interference from just about everything; you end up with WAY less than what the provider says you will get. Also, they refer to "MegaBITS" while never, ever, ever, ever, EVER making any clear distinction to the consumer about the difference between a bit and a byte (8 bits = 1 byte; most basic encryption is 8b/10b which cuts throughput, and more advanced can cut it further but it's getting better). That is why, when you download a file, you don't see "15,051KB/s" speed, but more like "348.1KB/s or 855.3KB/s".
For what it's worth, I have 50Mb/s home internet, and I get pretty close to advertised speeds due to tweaking and modifying stuff...
On my GNex, my absolute fastest 4G test has been 41.03MB/s down and 21.9MB/s up. That's WAAAY faster than my home internet, but testing my phone at home results in slower speed than WiFi the vast majority of the time.
Plus, WiFi saves your battery