No, I don't think Ralph set the fire that killed Pie-O-My. I think he is certainly CAPABLE of doing such a thing, but I don't think he did it.

I think this is a case of Tony becoming more compulsive and irrational, and hurting his business by being that way.

You gotta wonder about Tony. He was more than willing to kill Ralph over ALLEGEDLY killing a horse, but was actually debating over killing Ralph a year earlier, when Ralph DEFINITELY killed Tracee.

Mr. Soprano has his priorities a tad mixed up, I think.