True on both of those.
As atmosphere is lost into space (Such as not having much of a magnetic field, it needs to be replenished somehow.
I think Magnetic fields become less important the further you get from the Sun. Also, the stronger the gravity, the less important a Magnetic field.
Venus and Mars have extremely week Magnetic fields. This is probably one of the main reason’s Mars has lost so much atmosphere (Up for debate). On Venus, however, this doesn’t seem much a problem. Venus is loosing atmosphere do to this, but its gravity has helped hang on to most of it. Another factor may be because Venus has so much atmosphere (Perhaps more than Mars ever did).
(I wish we could put Venus in Mars orbit, and make Mars a moon of Venus)