It probably isn't as crazy as it sounds. Graphics consumed a considerable amount of the memory on early personal computers. It looks like one of those video mod

It probably isn't as crazy as it sounds. Graphics consumed a considerable amount of the memory on early personal computers. It looks like one of those video modes could consume about 75% of the 16 kB. Of course, that is cherry picking the most memory hungry mode. Other modes would use less memory, leaving unused memory for programs to use. If anything, it looks like the TI-99/4A is different since it appears to be designed for programs to use video memory because it's there and offers very little dedicated memory for the CPU.