It's a matter of convention, really. "string" string just looks more like C/C++ style. The general convention is to use whatever shortcuts your chosen language has provided (int/Int for Int32Int32). This goes for "object" and "decimal"decimal as well.
Theoretically this could help to port code into some future 64-bit standard in which "int" might mean Int64Int64, but that's not the point, and I would expect any upgrade wizard to change any "int"int references to "Int32"Int32 anyway just to be safe.