There are a few who still use the more classic T pose but one of the main reasons we use it is for compatability with walk designer. There's also the ease of clothing creation to factor in.  If you're ok with running a figure through walk designer and having the arms cross through the body and don't mind making things a tiny bit harder for content creators to build off of, there's nothing that says you can't have a model in a 45 degree T pose instead of a 90 degree one.