You don't need a card reader - the USB lead should be suffiecient (I say "should", as there were some crap leads sent with Wiz's a while back that didn't do what they should - charge/send data). The lead is significantly slower than a card reader though, especially for lots/large files.
A card reader will only set you back a couple of quid/dollars/euros at most, so there's no real excuse not to get one at some point.
TBH I'm a developer and I don't use a card reader (even though there's one built into my laptop and desktop) - I'm just too damned lazy to remove the card every time - I'd rather just leave it where it is and plug in the lead. Both methods are a pain in the arse really though, but the card reader is a quicker PITA