I suspect most people interested in software read Joel on Software. But his latest post should be read by all of us non-programmers. It’s Joel Spolsky’s interpretation of the future of the web. He calls it the innocuous Strategy Letter VI, but it’s really about learning from history.

Here’s the conclusion, but, as the saying goes, read the whole thing:

Imagine, for example, that you’re Google with GMail, and you’re feeling rather smug. But then somebody you’ve never heard of, some bratty Y Combinator startup, maybe, is gaining ridiculous traction selling NewSDK, which combines a great portable programming language that compiles to JavaScript, and even better, a huge Ajaxy library that includes all kinds of clever interop features. Not just cut ‘n’ paste: cool mashup features like synchronization and single-point identity management (so you don’t have to tell Facebook and Twitter what you’re doing, you can just enter it in one place). And you laugh at them, for their NewSDK is a honking 232 megabytes … 232 megabytes! … of JavaScript, and it takes 76 seconds to load a page. And your app, GMail, doesn’t lose any customers.

But then, while you’re sitting on your googlechair in the googleplex sipping googleccinos and feeling smuggy smug smug smug, new versions of the browsers come out that support cached, compiled JavaScript. And suddenly NewSDK is really fast. And Paul Graham gives them another 6000 boxes of instant noodles to eat, so they stay in business another three years perfecting things.

And your programmers are like, jeez louise, GMail is huge, we can’t port GMail to this stupid NewSDK. We’d have to change every line of code. Heck it’d be a complete rewrite; the whole programming model is upside down and recursive and the portable programming language has more parentheses than even Google can buy. The last line of almost every function consists of a string of 3,296 right parentheses. You have to buy a special editor to count them.

And the NewSDK people ship a pretty decent word processor and a pretty decent email app and a killer Facebook/Twitter event publisher that synchronizes with everything, so people start using it.

And while you’re not paying attention, everybody starts writing NewSDK apps, and they’re really good, and suddenly businesses ONLY want NewSDK apps, and all those old-school Plain Ajax apps look pathetic and won’t cut and paste and mash and sync and play drums nicely with one another. And Gmail becomes a legacy. The WordPerfect of Email. And you’ll tell your children how excited you were to get 2GB to store email, and they’ll laugh at you. Their nail polish has more than 2GB.

Crazy story? Substitute “Google Gmail” with “Lotus 1-2-3”. The NewSDK will be the second coming of Microsoft Windows; this is exactly how Lotus lost control of the spreadsheet market. And it’s going to happen again on the web because all the same dynamics and forces are in place. The only thing we don’t know yet are the particulars, but it’ll happen.