Tim O'Reilly writes:
"No one should be forced to choose open source, any more than they should be forced to choose proprietary software. And any victory for open source achieved through deprivation of the user's right to choose would indeed be a betrayal of the principles that free software and open source have stood for."
I think Tim's missed a crucial point here. This isn't about restricting user choices - it's about restricting vendor choices. Governments have long set higher standards for businesses which which they work than for businesses in general. Businesses have complained about this for years, but it's not much different from the kinds of centralized decision-making power that businesses themselves wield or that individuals wield.
If a company's CTO declares that all software purchases must be Microsoft or Microsoft-compatible, then that decision has a huge effect on subordinates who effectively lose the right to choose. The same thing happens if the decree specifies open source. Individuals often make the same kinds of decisions for themselves and their families. I don't see any reason why government should be denied the same privileges.
If vendors want to sell to the government, they need to comply with the rules the government sets down - accounting, labor, and licensing. The vendors might not like it, but for now at least the vendors don't run the government. This is a perfectly normal part of government, one of the ways in which a community can have its voice heard.
If part of the open source mission involves the complete decentralization of IT decision-making in government, then this is a betrayal, but I have a really hard time seeing it that way.