Why there is no 64-bit Silverlight plugin from Micorsoft:
In February 2009 we e-mailed Scott Guthrie, corporate vice president of Microsoft’s .NET Developer Division, and asked him if Silverlight 3 would have a 64-bit version. He told us no, as other browser plugins (and most browsers) don’t support 64-bit. Silverlight 3 was released in February 2009 and indeed was only available for 32-bit browsers.
Soon after the Silverlight 4 beta arrived (unsurprisingly, only in a 32-bit version), we spoke with Brian Goldfarb, director of the Developer Platform and Tools Group at Microsoft, about the company’s priorities for developing future versions of the plugin.
“The simple answer is no, we are not supporting 64-bit browsers,” Goldfarb told us. “Users are running 32-bit browsers because of plugins. It’s all about sequencing and timing. We’re absolutely going to do it; we’re just not going to do it yet.” Based on the data Microsoft was seeing, 64-bit browser support just wasn’t worth the effort, Goldfarb told us.
“I don’t know at what version, but it will happen,” he said. “My customers are asking for other features. We need to bring people into the 64-bit world, but the tradeoffs aren’t worth it right now. Businesses aren’t asking for 64-bit.”