I can see why you want a USB port for a table; transfer photos from cameras, share files via a flash drive, and a keyboard. I'm sure a 80% of the tablet market could find a use for USB port or USB adapter (I'm not a fan of the iPad adapter but it does work.) The added expense of the USB port would increase sales. The increase in sales would offset the increased cost of the tablet and increase profits.
I don't think a significant majority needs a HDMI port at this time. The number one feature of a tablet is it extremely portable; laying in bed or couch at odd angles is one reason why I use my tablet. Having it tethered to your TV sounds like a pain in the ass. It also means I'd have to carry a cable with me at all times or leave one plugged into my TV and hope others others have a spare HDMI cable with their TV. Non-slashdot people won't like that solution and their purchasing power is much larger than the slashdot crowd. Apple's Airplay or similar technology is the better answer but Airplay isn't supported by other manufacture (I'm 99% sure it is proprietary.) The small increase of sales would not offset the increased cost of the tablet and decrease profits.