Ya, that's pretty much incorrect info you were given.
The converter boxes are for, as you said, converting..specifically from Digital to Analog in order to work with older TV's that have NTSC tuners. You should be fine connecting directly. The converter won't give you more channels..it all depends on how good the signal is that the antenna is picking up.
This is a handy tool to see what you can expect:
http://www.tvfool.com/index.php?option=com_content&task=view&id=13