So your ISP connects directly to Biowares server? NO
You have no idea how many things are between your computer and their server. If anything in between has an issue then you will feel it.
Next time you experience the problem create a thread with a traceroute to your game server. Although traceroute isn't a good tool it can help give an idea of what is going on. It would also help to have a trace of things working as they should.
You have to realize, some just want to complain and nerd rage on others then accept any help in looking for a cause to the lag they have.
One person's lag issue doesn't mean its the next persons but some just do not want help.
It seems in this thread it has become it's a us and them , us that have no lag and them that do.
Below is an example of an issue in the first 4 hops and the effect it had getting to the dota server
2 tests from same ISP in the same city done within 2 minutes of each other with hop 7/6 onwards identical.
Complaint was constantly getting 100-170ms ping when his mates all had 30-50ms