Huh, really? I always figured piano had an unambiguous mapping from pitch to keys, whereas guitar typically has 2 or 3 possible fingerings for a given pitch. I find it pretty easy to get stuck with awkward positions on my first few times through a guitar piece--except those in which transitional notes are annotated with fret positions. Is that what you mean by "arranged for guitar"?
If the pattern is legato or fast and you can't lift up your hands, playing both G and A with the 5th finger will be difficult for most players. The easy solution is to finger the first triad with (1,3,4) or (1,2,4) so you can move 4 to 5. The latter being preferred if possible, to reinforce the weak 5th finger. (1,2,5 is probably the most natural fingering for the a-minor6 triad)
This is a trivial example, of course. With real music it's usually much more complicated and learning how to handle fingering challenges is one of the more important things you learn as a student of piano. Even classics often have fingering suggestions included, if not by the original composer than by subsequent editors.
No problem. I can't comment much on the initial comparison between tablature and fingering since I don't read tablature or more than the very basics of guitar.
It is true that if you map in the reverse direction, tablature can represent playable music even if it's not particularly expressive, while piano fingerings can not. (Well, I suppose you could write music with only piano fingerings and let the performer improvise, but I'm sure that's not the point of this discussion :)
Yes, string number/finger number positions are what I was referring to. And, as Goladus pointed out, getting stuck in those awkward positions definitely happens on piano, too.
