Better for the taxpayers.
Regardless, this sounds like an admission that the open source providers cannot provide a finished product capable of satisfying the govt's "exact needs".
I've worked on several government intranet projects as a military contractor. In those projects, the immediate assumption by the government is that it will run on Windows/IIS. That is often put out in the RFP. For the most part, all these people know is Windows, so that is all that is used. No other software platform even had a chance to show merits. When writing criteria for desktops, they will, for example, find some useless feature that only exists in Excel and state that as a requirement. I've both written and responded to these things, I know how they work. You can effectively eliminate open competition by carefully wording the purchase order or RFP.
I'd rather see the govt buy software licenses than hire an army of programmers in a "ministry of open source software development".
In that context I was speaking as government as customer, not as developer. When it comes time to pay $50 million for the next batch of Windows licenses for a government agency, they WILL NOT be looking to an alternative that could save them money. They will simply renew the licenses using our money.
I've been both the beneficiary and non-beneficiary of, [ahem], "targeted" specifications... So I know what you're talking about. :-)
But the solution isn't to legislate a preference for open source software. That's no better than the very thing you're complaining about.