If your Comcast internet is much slower than advertised, there's a problem, and it's likely fixable. It can be bad cables or splitters in the house, poor signal from being too many splitters from the source, a bad modem, wrong service settings for your account on Comcast's end, many things. If you call Comcast and are willing to do some serious troubleshooting with a technician at your house, you should be able to get the advertised speeds. I've done so at 7 different homes in the past 6 years, but only after doing some work at each one.