I think it does. Managed network security services is one arena where size is always a factor, and bigger is usually better. With more employees you have more analysts per shift. You have more customers, so you see more of the Internet. With enough customers your view of the Internet begins to resemble a statistically significant sample, from which you can make inferences about the health of the global network.
I thought this Dark Reading story on the merger (the new company will be called SecureWorks -- no more "how do I say LURHQ?") had an interesting quote:
But all of this doesn't mean IBM-ISS isn't on SecureWorks' radar: Prince says SecureWorks' main competitors on the enterprise side are Symantec, VeriSign, and "now IBM." On the commercial side, it will be local telcos and other service providers, he says.
Where is Counterpane? They must be desperate for a buyer. I expect to see more MSSPs combining to form Voltron as time progresses.