He's saying simplicity FOR THE USER is tough to build. I'm sure even more so when they are backed by complex logic that make them magic for the user.

Maybe you should work on your own reading comprehension skills before you go insulting other people's.

It still doesn't make sense. To extend my example, the interface into all search engines, google or otherwise, is naturally simple. The more complicated interfaces, like that of clusty.com or a9.com, are surely not easier to create.

Sure they are! Complicated interfaces make it easy to:

1 - avoid forcing yourself to really prioritize your feature set, something that's really hard to do and requires really understanding your users.

2 - push a bunch of effort from you to the user.

For example, you cited A9.com. If I do a search on A9.com, the search results window is split (by default) into two parts: one that lists web search results and one that lists book search results. At least by default, it appears that both sections are always there.

If I do a search on Google, than Google will usually only display web search results, but if it senses I'm searching for something about a book (example: do a search for "Charles Dickens"), you'll sometimes see some book results up at the top.

Google's method of only showing you book results when it suspects you are looking for something having to do with books is both much less complex for the user and much more difficult to build.

Looks like sometimes that 140 character limit is a problem.

I've seen a funny result of the 140 limit + the stack of comments. People will leave three part tweets, often numbered, but will need to do number 3 first.

One thing people love about twitter is the ability to push updates to everyone. Everyone wouldn't tolerate it for long messages, but the desire is clearly there on behalf of the senders.