You want the filter to be formed from the 2 resistors and the differential capacitor. Its easy to get 2 fairly well matched resistors, and if there is only one capacitor matching is not an issue there. Now you have rolled off the input signal nicely, in a way which should be fairly consistent, even if your capacitor varies quite a bit with temperature. The balance of the filter means it won't cause a phase shift. However, there is another issue to deal with....
The CMRR of most sigma-delta converters is really good. Some of the switched capacitor input ones can have an amazing CMRR. However, they usually have one weakness in their input rejection - high frequency noise, beyond the bandwidth of the input circuitry, isn't rejected very well. That's why its a good idea to have small equal value bypass capacitors from each leg to ground. They will suppress RF pickup. Low value capacitors usually work better, as they perform better at high frequencies. Also, capacitors large enough to form an effective part of the anti-alias filter would need to be accurately matched, so they don't introduce a phase shift. You want these two capacitors to have their ground sides connected directly together. If they ground to different points in the circuitry they can inject any ground plane noise that may exist as a differential signal. Keep the grounds physically adjacent, and they can only input noise common mode. Keep them small, and any tolerance mismatch between these capacitors is seldom sufficient to spoil the circuit's balance enough to be troublesome.
So, I don't know why they recommend a 10 times ratio in the capacitances. A 1000 times ratio is usually a better solution.