system.webServer/httpCompression has property noCompressionForHttp10 whose default value is true. Setting it to false will enable compression for http 1.0. This property is not exposed through UI. You can use the following appcmd command to set it (run in elevated command window).
%windir%\system32\inetsrv\appcmd set config /section:httpCompression /noCompressionForHttp10:false
Thanks,
Kanwal