You must be a romantic, they way you talk about old pianists practicing on out-of-tune and broken pianos in small apartmentes they had to share with AT LEAST ten other families!:-)
Chopin composed his Preludes on ...an upright! It's still there, on Mallorca.
Anyway, grands differ hugely from one another, as do uprights. But if you are thinking about these things, you should know what's actually different:
* On a grand you play against gravity when pressing the key;
on an upright you play against the force of a spring.
*On a grand, the una corda shifts the mechanics so that the hammers strike two instead of three strings for each note in the treble;
on an upright it moves the hammer assembly further towards the strings, and causes an unwanted lost motion.
-In both cases, the aim is to create a softer sound.
* The middle pedal on a grand (only a few are fitted with one) is to sustain only selected notes; on an upright it is as Andy says, pulls down a mute ("practice" mute, not to disturb neighbours!)
The original construction of the piano was like a grand, later, during the 19th century, they invented the upright as a clever solution to people with limited space; thus, a piano you could simply put against the wall. Similarly, the "baby grand" was another attempt at increasing the sales, nobody built any such in the beginning.
I think the greatest limit to an upright is the una corda (where did you get the idea that they are disappearing?), which is something you cannot really use as originally intended, due to the lost motion.
Otherwise, on a well regulated upright you'll be just as able to practise trills, pianissimo, staccato, legato, any pianistic technique you can think of. But, mind you, well regulated it must be!! Same for a grand, by the way...
To follow your logic the other way, would imply that at the end you'll need a Steinway D to practice on, to learn how to play on a Steinway D.
Which is what most rich and famous concert-pianists end up buying, of course...
Topic: is a grand piano really necessary