Of course they do.
1) Semen is ejaculated in steps. Your tubes and shaft fill up, bit by bit, until you shoot. So a guy with an 8 inch member has a much more heightened experience than a guy with 4 inches, as the semen builds to climax. Basic logic.
2) Longer penises are usually thicker too, which means they're made up of more muscle. That means there's more muscle contracting at the point of ejaculation, so this big, thick shaft is just buzzing with pleasure, when combined with factor one. Thicker penises are tighter within a woman's holes, and so friction is much greater than for other men. So for a big member up a woman's hole at the point of ejaculation, it feels awesome for all that muscle to have the added friction of her tight walls. Again, basic logic.
3) When you have a big one, the woman is in awe of it, and you have no inhibitions. This point is psychological. At the point of ejaculation, you are free of any insecurity and just let your big, thick, powerful member spit all over your girlfriend's tongue and breasts, knowing that she sees you as so much more masculine than her five-inch ex, and that she'll always come back to you for more. Combine this with factors one and two and there's really no longer a question of whether big members feel better when they spit. It's obvious.