MSSQL10_50.SQLEXPRESS vs MSSQL10.SQLEXPRESS

Hi there

I have an Windows App (VS 2008 using VB) deployment prerequisite of SQL 2008 Express. I recently installed my App on a Windows 8.1 x64 system and all worked as expected. The only real difference I see is the SQL Express Folder name on the deployment system (Windows 8.1) is "MSSQL10.SQLEXPRESS" whereas on my system (Windows 7 x64) the SQL Express Folder name is "MSSQL10_50.SQLEXPRESS" . Can someone explain why the difference?

Thanks

Dweezil