I have a VAIO VPCEA23EN laptop with ATI Radeon H 5145 graphics but when I installed the drivers from Additional Hardware (proprietory drivers) its showing it as ATI Radeon HD 4500. Video quality is also not as good as that when I play the same video in VLC in Windows 7.
try installing VLC version 2.0 for Linux. Also sometimes th gfx hardware model shown through Ubuntu's detection mechanism maybe a bit different but dont worry they're 100% compatible.
Reason being: your gx card model belongs to a series (in terms of the core chip thats on 54xx/45xx) such as 45xx gfx series and the exact model is 5145 etc.
So just dont worry about just straightway head over to Ubuntu's update. ALSO you can try installing the gfx driver by downloading it from ATI's website directly.