The amount of people that ask whether it’s mandatory to buy a SU-WL31 mount if they want to wall mount and have bought a Sony LCD is mega huge. Most of these people feel manipulated into having to, and are worried that the SU-WL31 mount is the only mount that will fit their machine. It’s not true.
A mount needs to take back stage in the relationship between mount and LCD. All a mount needs to do is fit your machine and be strong enough to hold it. Given that the majority of the time you can’t even see the mount, as long as it works practically speaking, it doesn’t matter what make it is.
Before you feel railroaded into buying a SU-WL31 mount, then have a shop about. Type in the model number of the set you want to mount into Google and see what recommendations come up. It’s very likely you’ll be able to get a mount just as good as the SU-WL31 mount but for half the price.