You might have to play a bit with the brightnes/gamma in some picture program, but several of the pictures clearly show a triangular shape for the inside edge. I think I even read from someone that at the bottom it was 1/8 and near the top it was an inch or half an inch wider. Can't find it anymore unfortunately.
I see a clear increase in width of about half an inch in the Ms Pac with the dimensions (after correcting for perspective). On the other hand it could be a problem with the camera too since the back bulges out from a perfectly vertical line too. It's not easy to see 1/2" on a 30 inch from a small picture. In the MsPac example it's just 5 or 6 pixels or something. The inside leading edges on the ms pac cabs are pretty clearly visible though and I'd say in some of the Galaga pictures I posted it's pretty clear too. There is some flash and perspective as well, but the leading edge is visible against the kickplate falling back further.
I'd say it's most clear on the clear pac

That was a reproduction done for a museum. There is no way they made that slope by accident (or from the plans of jakobuds site)
CheffoJeffo's picture looks perfecly straight yes (after the picture is corrected for perspective)
It's not really about being 100% accurate, but the front slope alters the appearance of the cab. I guess it doesn't matter no, but for instance there are so many pacman cabs that are repainted, stickered and are now sold as "original" Galaga cabs. It just looks so different. Maybe a slightly different profile is not important, but it just looks weird to me.
Personally I think the sloped front makes the cab look better too. Somehow it looks slimmer and less bulky to me Guess it doesn't make sense since it only adds to the side profile, but still.
What I really wonder about is where Jakobud's dimensions came from. Someone most have measured his/her cab and can verify if it is actually sloped or not. Maybe that was from an MS Pac cab even. Maybe only MsPac cabs have the sloped front. It's nearly impossible to tell an MsPac cab from a Galaga cab if that would be the only difference and I guess many Galaga cabs on eBay will have been MsPacs once too.
Who knows. Maybe it's just an MsPac thing.