Windows Phone 7.5 doesn't let you link directly to HTML content in your xap or install file in the market place. To make this work all this content needs to be copied to isolated storage. The HTML App Host Framework provides in frastructure
for doing that but also only does it once so each time the app loads its not copying everything into isolated storage again. To deal with new versions of your application there is also a property for letting the HTMLAppHost know when to re copy everything
into isolated storage called 'CurrentAppVersion'. Where you use the HTMLApplicationHost control you could have somethingthat looks like this:
<HTMLAppHost:AppHostShell x:Name="AppHostControl" Source="/index.html" CurrentAppVersion="1"
ScriptNotify="AppHostShell_ScriptNotify" Grid.Row="1" />
Each time you deploy a new version to the market place you then increment the value 'CurrentAppVersion'.