How can a different mains lead help a TV which is digital and uses a switched mode power supply (which converts AC to DC back to AC and finally into DC again). Even if you buy into the debate about higher quality mains leads providing a "cleaner" power path, then it can still only provide this higher quality path between the TV and the wall socket. All the wiring throughout your house, from the wall socket to back to the consumer unit is almost certainly standard solid core twin and earth cable which costs less than £1 per meter, so the power "quality" is already limited by that wiring, not to mention the cables and power transmission equipment between your house, the national grid, and the power stations.
If you could do a double blind test comparing standard power cable with the expensive specialist ones in a normal home/office, then the results would be pretty much random.
Save your money for better interconnect cables, better source equipment, beer etc.