The ppa you referenced is not for Steam, it is for the x-swat team.
The x-swat ppa is for the latest stable driver that are available for Ubuntu. Ubuntu 13.10 just came out and as a result, it already has the latest stable drivers installed.
The reason that you are getting an error on the x-swat ppa is that it is not set up yet(404 errors are "not found"). There would be no reason yet for there to be a 13.10 x-swat ppa, as there would be nothing to put in it. It is also possible that they are in the process of setting it up, it takes the ppa owners some time to get the ppas set up for a new version, sometimes they have to fix bugs that pop up in the new release, which slows them down further- that is one of the drawbacks to upgrading as soon as the new release is out, many wait a few weeks or more to let these kind of issues get resolved before upgrading.
From your question, I cannot tell but I assume that Steam itself is working fine(you don't specify), bu that you tried to add the x-swat ppa and now are getting this error. If you installed the ppa because Steam gave you the pop up when starting that recommended you enable that ppa, you can just disable the ppa and ignore the box for now. I think that Steam looks to see if that ppa is enabled by default and upon not finding it will give you that box upon starting; it is likely that this only happens with Intel cards but I don't know for sure(I only use Intel so I cannot test is to be sure)
To make the ppa warning go away,
Open the Update Manager
On the lower right click on Settings
Under the Tab Other software click on the box next to the listing for the x-swat ppa
A box will pop-up asking for your password, after entering it the bos will be unchecked, disabling the ppa, there may be another line just below or above for the "x-swat ppa (source code)", make sure you disable it too or it will still give you the error.
- You could also just highlight the ppa line then click Remove instead of disabling but you would have to add it again later, either way is fine.
You can now close the current window. When back on the Update Manager click on the update button to refresh your sources to complete the removal of the x-swat ppa.
There may be a way to get that box that pops up when Steam starts to go away, I can't remember if there is a "Don't show this again" button on that box or not. If there is not, I'm not sure if you can stop it, you may have to just close it every time.
If you want to manually keep an eye on the x-swat ppa to see if they have added Saucy to the ppa by checking https://launchpad.net/~ubuntu-x-swat/+archive/x-updates When they add it you will be able to select it in the drop down menu under "Overview of Published Packages" at the bottom of the page. When Saucy is supported, you can then either re-enable the ppa or add it again, if you removed it.