Yes a codec pack is still needed, we recommend something minimalistic like ffdshow tryouts (you need the 32 bit version even with 64 bit Windows).
With regard to Go Pro movies on PS3, GoPro produces MP4 files and such files are delivered to PS3 as is (i.e. not transcoded), It seems like the PS3 cannot handle them (probably due to the high bitrate) and so the only solution would be to force transcode them. Did you try that?
First make sure that indeed they are not being transcoded by looking at the status page of the GUI under transcoding and making sure the video is not listed there. Then install the codec pack, set the folder in which the movies reside to "always transcode", restart PS3 and try again.