Yep, Gus has it nailed. Management Studio is making that conversion. Plus, in the engine, SQL Server itself is using a binary to deal with execution plans, not XML, so there's a conversion to XML taking place there and then you get the XML which is converted to graphical. You can look at the XML again by right clicking on any graphical plan and selecting the XML menu choice to see the raw data.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning