I've not noticed it, but I generally don't shoot more than 50 rounds per pistol in a trip & it may be a mixture of brands, some reputed to be dirtier than others. Also, I tend to take only my 1911s or only my Bersas, so when I clean them up, I don't have a side-by-side comparison.
I'm wondering if this might pertain to most imports, as compared to home grown pistols. I know the importers have to jump through a lot of hoops to get their firearms okayed for import. They tend to do things to gain 'points' with ATF that domestics may not have to do.