I'm not sure I understand the question. Your question assumes that the "3rd party development platform" has an inherent advantage over .NET, so the use of .NET must be justified.
Microsoft's licensing costs are still among the lowest in the industry. Setting up an enterprise class ASP.NET application with Windows 2000 (or 2003) that uses Active Directory and SQL Server 2000 as the backends is still FAR cheaper than using, say, BEA's WebLogic and IBM's DB2 or an Oracle database.
In fact, the article mentions just this: "this price, SQL Server is still dramatically less expensive than DB2 or Oracle and outperforms both of them, according to the latest TPC-C benchmarks."
Of course, I would also challenge the assertion that there are "3rd" party tools that have the same capabilities as .NET. While J2EE certainly allows you to do everything .NET does (with a few notable exceptions), it takes more time and more money to develop the same application on J2EE. (Typically.)
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