Q4Max adds many features and fixes to Quake 4, making it a much more enjoyable and complete game. For this reason, most servers running Quake 4 are running Q4Max.
The voting system in Q4Max is significantly updated from the base Quake 4 system. There are many more vote-able parameters. This makes many features accessible to players - such as the "start weapons" vote which is highlighted here, which allows them to change the weapons available at spawn time.
All votes can be disabled by the server administrator, so what can be played on their server is still up to them.