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Sami, I am not sure if you are referring to me.
In any case, you are wrong in your first post. Every lens design will have a different degree of blur at the same aperture. Some lenses have a lot of depth of field, others much less. The lens design is everything. The DoF calculators are only indications of how much DoF you might get, not accurate calculations. They are based on averages, or the thin lens simplification.
Many lenses appear to be very similar, simply because most lenses are based on the same designs. The double-Gauss design for example. Only those lenses which have significantly different designs will have significantly different DoF, and the two lenses I listed belong to this group.
Personally compare the 50MP@f/2 to the 50 Planar @ f/2 and you will see that I am right. The 50MP has a lot of depth of field for a 50mm lens, even at the same aperture as many other lenses. The 21 Distagon also does. I haven't tested this much, but I am thinking that maybe one or both 25mm lenses do too.