The idea of the "piano arrangement" is a funny subject to me. Of course, I understand what it is, it's what happens every time I play. I don't think about it with that vocabulary, however, until someone says something like: "That was a nice arrangement you just played" "Well, that's good", I think, "I wonder how it went?". It all ends there unless the one who initiated this continues: "Where did you get it?". "Huh?", I think. At that point my mouth may start moving: "Where did you come up with that sentence? Did you read it? Who wrote it first?". If I'm smart (this often eludes me), I wrap it up quickly, talking about musical improvisation as conversation, or dialog, or pontification (solo pianists can be pontificators - gee, sounds sinful).
Of course, what people are referring to are the sheet music arrangements you can buy, of most any thing ever written, if you look hard enough. I don't use them. Why would I? We (of whatever particular group I'm referring, I'm not exactly sure) improvise an "arrangement" every time we play a tune. No point having someone do for me what I'm already doing (kind of like having a "conversation coach", I guess). On top of that, I like that I can express myself. It is uniquely my communication. I guess you can say that jazz (at least with me) "eliminates the middleman".