Why so reserved? Maybe it’s because Sony (SNE) is struggling through yet  another restructuring, so a big party would seem inappropriate. Maybe because Sony views the Walkman’s birthday as a lot of middle-aged people view their birthdays: Markers of bygone eras and missed opportunities. Or else it’s just Apple’s (AAPL) fault. Associated Press:

The manufacturer, which also makes Vaio personal computers and Cyber-shot cameras, hasn’t had a decisive hit like the Walkman for years, and has taken a battering in the portable music player market to Apple Inc.’s iPod.

Sony has sold 385 million Walkman machines worldwide in 30 years as it evolved from playing cassettes to compact disks then minidisks — a smaller version of the CD — and finally digital files. Apple has sold more than 210 million iPod machines worldwide in eight years….

The archival exhibit shows other Sony products that have been discontinued or lost out to competition over the years — the Betamax video cassette recorder, the Trinitron TV, the Aibo dog-shaped robotic pet.

I do remember hearing some Sony folks mutter hopeful words about a new line of Walkmans that came preloaded with music from Sony artists like Beyoncé and were supposedly flying off the shelves at Wal-Mart (WMT). But that was a while ago, come to think of it, and I haven’t heard about it since.

In any case, just because Sony’s being bashful about the Walkman’s history doesn’t make it less interesting. You can learn more about it at Sony’s online archive, which is compelling despite the fact that it’s a stilted corporate hagiography. Start reading at Chapter 17, part 2: “Listening to Stereophonic Sound While Walking.”