Yes, your right =X=, but the Sprint plan is truly unlimited for the EVO 4G, and I believe other 4G phones. The caveat is that there is a $10 surcharge for 4G phones. Mobil HotSpot is another $30/month, I turned that off when I got my SGT. Since Sprint does not yet have a 4G tablet, I'm sure the pricing will be tweaked when the HTC Flyer (EVO View) is released this summer.
The EVO 4G is so battery intensive when 4G is turned on that unless you have a charger handy it's largely useless, and Mobil HotSpot is an added drain. If you plan to do much tethering in 4G mode, you might just as well plug it in to a USB port and use USB tethering (free) just to keep the battery charged.