1) Pianos were made from the ground up to be idiot-proof at a beginner level. This hasn’t lowered the standard for the instrument; instead, it seems to have raised it. Since it’s fairly easy to use at low levels, one must play it particularly well to garner any attention. Contrast that with Ruggiero Ricci’s statement that even playing a violin in tune with good tone and timing is high-level playing. Like xkcd says, our brains have one scale, and we resize our experiences to fit (mouseover to see this comment). Move the bar for acceptable beginner play down, and it just makes the bar for virtuoso play that much higher.
2) This beginner-friendliness has made the piano welcoming to all forms of music, secular and popular as well as classical and liturgical. They have been designed for tone and massiveness of sound, but also for home and apartment convenience as well (making them more available to people without much money, which is the biggest driver in my mind for digital pianos). Thanks to this, taverns, juke joints, speakeasies, and private homes were the bailiwick of the piano as well as the concert hall. The piano was the Victorian/Edwardian jukebox and home stereo, and as such it welcomed pop songs, drinking songs, patriotic songs, and prohibition songs, blues, jazz, and any other genre, equally. Sixty years after Jerry Lee Lewis was pounding pianos into splinters, people are stunned to hear 2Cellos play Michael Jackson covers. Classically trained pianists who played pop and rock have been around since the days of Neal Sedaka and Billy Joel.
The beginner-friendliness has also made it possible for valuable things at all ability levels to be communicated through the piano. I’m a strong believer that there are things of value to say at all ability levels, and that includes beginners. The piano, more than any other instrument, allows these things to be said. A beginner pianist may be someone with far more life experience than someone of much greater ability. How nice that a piano can allow both to say something.
3) Pianos are children of the industrial revolution, and aware of it. They were perfected by mass production, with many tiny moving parts. The deBeers-commercial-like romance of the individually crafted artisanal device does not exist for the piano, although there’s money snobbery, and gawd knows Steinway tries hard to inflate it. (Before the advent of steam and then electrical power and mass production, they sounded like crap. Strings broke. Keys broke. Franz Liszt may have smashed up old-timers, but even he wouldn’t make a dent in a modern concert grand.) Consequently, we do not try to hide the fact that we are machine operators and must empty our souls into the devices in order to play rather than to mysticize the devices themselves as having souls. Furthermore, robots have been playing them in the form of player pianos for roughly a century. Meanwhile, Yamaha’s violin- and trumpet-playing robots have caused minor conniptions and defensiveness among violinists and trumpeters.
Honestly, from the point of view of a pianist, the way that string players treat their instruments like stone idols seems strange. The mysticism strikes me as not entirely healthy, and the way that the good instruments are priced so astronomically out of reach of the best players is horrifying to me. It’s counterproductive to force communicative artists into a position of subservience to someone of great wealth and power, as the painful example of Dylana Jensen shows. No one can pull that kind of bullshit with a pianist, thankfully.
4) Pianos are fungible. Some are well-regulated, well-voiced, and properly tuned, and many are not. But to be perfectly honest, any well-regulated, well-voiced, well-tuned piano is pretty much serviceable for anything. Sure, a virtuoso with good ears can prefer one sound over another, or consider one sound more suitable for a certain type of music, but in general … a piano is a piano is a piano after a certain standard of operability is reached.
I often bitch about the fact that a pianist has to be very careful to put life into a piano in order to not come off as a corpse puppeteer or machine operator. But to be honest, there’s a lot of good to be said about an instrument that was designed to be kind(er) to the body, kind to beginners, unashamedly mechanical, and welcoming to all forms of music.
I’ve carefully not gone into the way that pianos can carry enormous abstract complexity; I’ve talked about that before.