Is Windows PowerShell 2.0 installed by default on Windows 7?

You don't need to dig it out of the registry keys. Just run get-host and check the version.

You can also use $PSVersionTable

PS > $PSVersionTable

Name                           Value
----                           -----
PSVersion                      2.0
PSCompatibleVersions           {1.0, 2.0}
BuildVersion                   6.1.7600.16385
PSRemotingProtocolVersion      2.1
WSManStackVersion              2.0
CLRVersion                     4.0.30319.225
SerializationVersion           1.1.0.1

This var exists only in PowerShell V2.0 and gives th CLR version you use. Normal result is:

PS > $PSVersionTable

Name                           Value
----                           -----
CLRVersion                     2.0.50727.4959
BuildVersion                   6.1.7600.16385
PSVersion                      2.0
WSManStackVersion              2.0
PSCompatibleVersions           {1.0, 2.0}
SerializationVersion           1.1.0.1
PSRemotingProtocolVersion      2.1

The location of the PowerShell executable and supporting files wasn't changed for V2, nor was the .ps1 script extension because V2 is fully backward compatible—it replaces V1 rather than needing some side by side mechanism.