This is not always true. I know a serial entrepreneur who wouldn't know HTML from e-mail but he is a great salesman. Basically he has sold the project, signed the contract and has the money in the bank before the first line of code is written. I would recommend any coder I know to take a 10% share in a startup he launches in exchange for building the thing.
The key point here is that there are just as many lousy business people as there are lousy programmers. Often programmers don't know what to look for in a business guy, and end up with one of the lousy ones that are full of hot air and no substance. This goes the other way as well which is why a lot of business types end up with lousy programmers in their startup.
Being able to bridge the gap and walk both roads is worth more than gold.
When starting out the business or marketing types don't bring much value unless they actually have $ to pump into the start up.