According to this documentation you don't have your Registry search parameters set up quite right. The following should yield better results.
<Property Id="NReportViewerV10">
<RegistrySearch Id="NetFramework20"
Root="HKLM"
Key="SOFTWARE\Microsoft\ReportViewer\v10.0"
Name="Install"
Type="raw" />
</Property>
<Property Id="ReportViewerWow64V10">
<RegistrySearch Id="NetFramework20"
Root="HKLM"
Key="SOFTWARE\Wow6432Node\Microsoft\ReportViewer\v10.0"
Name="Install"
Type="raw" />
</Property>