'Rizon' and 'Modemnet' are differnet servers, as a result have differnet "services" they offer, while Rizon may offer you nickname registration and prompt for your password when you connect, Modemnet may not.
As far as a +v goes, a +v is temporary on most servers but can be automatically given on others, the reason your +v disappears is because you obviously arent given it automatically (by either services or an op) but other people are, usually because they have been there longer and are well known.
Eamonn.
