The signal in the phono cable is very low. Any rfi or hum can easily interfere with the signal. Balanced cables tend to cancel out this type of interference.
The signal from a phono cartridge is basically a balanced signal, so going with an all balanced system makes sense. Ralph Karsten, with Atma-Sphere, can probably explain it better than I can. (Ralph designs his preamps primarily to use balanced connections, including the phono inputs and outputs.). I suggest you contact him. He is very knowledgable and very helpful. (A true gentleman, IMHO. And this coming from a guy who doesn't even own any of his gear, although I certainly wouldn't rule it out in the future - especially his MP-1 preamp.)
FYI: I use balanced connections from my tonearm cables all the way through to my amplifiers. I am very happy with my system and have no plans to ever go back to single ended connections.
Kurt is correct . . . except for some very rare instances, a phono cartridge is always wired as a balanced connection - it can be thought of as a transformer with a mechanical (rather than electrical) primary. And given the ratio of a cartridge's common-mode versus differential-mode source impedance, the interconnection to the preamp can retain most of the noise-rejection performance of a balanced line even if it's terminated to an unbalanced input.
There's very little performance difference that's associated with the XLR-vs.-RCA connectors themselves as they're the same connections . . . for conventional RCAs, the separate ground wire is used in place of pin 1 on the XLR, and the tip and ring of the RCA correspond to pins 2 and 3 respectively (American standard; European standard reverses pins 2 and 3).
For the cable to the turntable, using shielded-twisted-pair construction helps preserve the impedance balance, and thus improves immunity to magnetically-induced hum. The tradeoff is higher capacitance, and for MM cartridges this can be a problem . . . so personally, I prefer simple coaxial phono cables of as short as practical for MMs, and shielded-twisted-pair for low-output MCs.
For the phono stage, so much of it is the designer's preferences for the particular topology, and whether or not it lends itself to a balanced input . . . because the balanced nature of the cartridge can make the noise rejection similar between the two. One can't escape the fact that an active balanced differential input generally a minimum of 3dB noisier than an unbalanced input, but whether this ends up being significant in the context of the entire circuit is another matter.