Well on Baleno its more of marketing gimmick if its the original "marka". Or the owner just used it on his own.
It originated in Italy as GT and stood for Grand Turismo. For performance/ sporty suspension and so on.
GTI which is also known as Golf GTI in europe. Its a performance varient of Golf. Golf is VW most sold car all over world. GTI earlier generations engine was fuel injected so it was known as GTI. I stands for injection. VW since last 2 generations its FSI ( fuel stratified injection) or TSI engine. turbocharged stratified injection (TSI).. Both FSI and TSI are turbo charged.
VW wanted to keep the heritage GTI name so that's the reason they are still using it. now since 2009 in USA it 2L TSI.
you can read about TSI here http://files.engineering.com/download.aspx?folder=4188e34f-2b48-49fa-9c9d-e2ed7ac676a3&file=VW.COM_2.0L_TSI_Turbo_SSP_824803.pdf