Ok, Most modern flat screen TV's do MPEG4 just fine. It's the "Standard" video format for Windows computers after all.
What has happened is SOME cable companies are now Encrypting and you need a set top decoder.. This may have happned along with a switch from "Mostly analog" to Digital.
ORiginally cable systems were analog
Then they went to a digital format called QAM (Quaduature Amplitude Modulation)
Then the world went digital for broadcast
Some Cable companies pass on ATSC Some QAM and Some digital and most mixed.
QAM allows for encryption Most modern TVs (one brand is notabally and exception) DO NTSC (The old analog National Televiosion Standards Comittee or Never Twice Same Color take your pick)
ATSC (American Television Standards Comittee) Digital OTA broadcast
QAM But NOT QAM encrypted
ANd MPEG (via the USB port)
ELEMENT TV... the only one made in the USA and I'm not sure if they still are as some plants have been closed.. IS also the only one I know of that does not do QAM.