Ask HN: Why do web-startups need tech co-founders?

There is alot of talk about the importance of technical co-founders in web startups.

And yet, during a long conversation I had with a group of "founders", I could not manage to explain the rational behind the argument.

Their view was:

    1. We get some seed money (they had good connections)
    2. Hire a designer and developer
    3. They build the site
    4. Later we keep them for support and improvements (and maybe hire more to expand)

How would you explain to someone why a web company needs a good technical lead (preferably co-founder) and can't just go "hire someone to write the site" ? .. or maybe they dont ?

EDIT: "In other words, what can a co-founder do that an employee cant ?"