Characters are only allowed to purchase two weapons, so why would the basic infantry be allowed to have more than the characters?
Characters are only allowed to *purchase* two weapons from the *armoury* according to the *old* codex.
There is not now, nor has there ever been any limitation on the number of weapons any one model may actually *have* only how many extra weapons they may purchase.
The old codex limited how many weapons you could buy, bot the core rules says nothing about how many you can carry.
The new codex has no armoury to speak of, and therefore no restrictions except where listed in the unit's options. All Chaos SM are equipped with a pistol, a chainsword and a bolter. All at once.
This is what holsters, scabbards and carrying straps are for.
Now, they do go out of their way to say that certain weapon options will replace your weapons now (May replace bis bolt pistol with a plasma pistol, for example) but other than that, there's no artificial restriction telling you how much gear you can carry.
Likewise, chaos bikes no longer give a bonus attack...BUT they no longer deny you an extra attack for having 2 CCWs, so chaos bikers (who get both pistols and chainswords) still have a bonus attack.