I agree, for a beginner, as long as it can be tuned correctly, and as long as the keys are not damaged, it doesn't matter. Of course people will tell you what the "best" brands are and if you want to spend the money, you can always go ahead. But it's really not necessary.
I did piano for years and years, thought of becoming teacher qualified even (probably only a year or two extra study for me), and our home piano was a nearly antique "pianola" (the piano that can play rolls when you pump the pedals) - I have no idea how old it is, it was my great uncle's and we got it when he passed away when I was a kid...
I would LOVE a grand if I ever had the money/space for one. I do think they sound better and are more enjoyable to play. But I view it as a luxury, not a necessity. As long as it is in tune and isn't damaged, that's really all that matters...