I'm reading on Jubjub, which is planned for the next upgrade of Zcash. It is based on a Twisted Edwards curve with parameters $a = -1$ and $d = −(10240/10241)$. The reading says Jubjub does not need projective coordinates because inversion is cheap.
My question is, is the "cheap inversion" property that of Twisted Edwards curves in general, or the parameter selection of Jubjub in particular?