“It’s called the “equities issue.” Basically, the NSA has two roles: eavesdrop on their stuff, and protect our stuff. When both sides use the same stuff — Windows Vista, for example — the agency has to decide whether to exploit vulnerabilities to eavesdrop on their stuff or close the same vulnerabilities to protect our stuff. In its partnership with Microsoft, it could have decided to go either way: to deliberately introduce vulnerabilities that it could exploit, or deliberately harden the OS to protect its own interests.”
That might (should!) probably influence some corporate buying decisions. Especially those of non-US companies.