I know what you mean, and although it's been explained to you how it works in Prologue, the main argument or objection remains, that's why I created this thread.
Hopefully it provides some more insight as you're not alone in wishing for more accurate automatics.
https://www.gtplanet.net/forum/showthread.php?t=125469
Thanks for the link. Interesting reading. It seems we share a similar opinion on the subject.
We can only hope that PD has put an effort into simulating automatic transmission accurately. I'm glad you guys helped me realise the root of the problem. Shifting paddles or not doesn't really matter as long as every single cars basically behaves like it uses a manual transmission.
However, if PD has included a realistic simulation of automatic transmission, then my initial concern gets back on topic. Manual shifting should not be allowed in cars using a traditional automatic transmission without modern technologies such as Tiptronic or similar. While this is not the case for cars such as SL55 AMG, it could be a problem for older cars in GT5.
We all know that manual shifting is an advantage in racing. So it would simply be unfair if the game allowed us to shift manually while that wouldn't be an option in the real car using a traditional automatic transmission. Allowing automatic transmission in a car with a manual transmission is a different story though as there is no advantage to gain and neither does it add any unrealistic abilities to the transmission.