Why Not Use PC To Make Glass Cockpit?

Standard disclaimer applies: I still have my copy of Flight Training
next to the porcelain throne. Ahem.

However, as I flip the pages of this magazine, I cannot help but think
that companies like Garmin are getting off a bit easy.

Being a software developer, I am very suprised to discover that not
every aicraft costing over $30,000 has a full-featured glass cockpit.
Unless I am missing somethnig, it appears that everything that a pilot
needs can be made with very very cheap hardware.

A PC can be had for under $500 easily, the mother board for even less.
There are software programmable radios that can be made for under $100
that can tune into any frequency under 1GHz (in other words, if it's
there and not encrypted, you can get it). There are USB sensors of all
sorts (altitude, humidity, wind speed, etc.) And good software
engineers can write pretty much any piece of software that is required
so long as they receive guidance about what is supposed to do what,
with pictures of twirly things to on the display to keep the pilot from
getting bored.

So I am wondering, why isn't anyone doing this on a grander scale. Are
they?

-Chaud Lapin-