Some of the American valve makers did promote the use of such specialized triodes in VHF as well as in UHF TV tuners in the early-to-mid 1950s. For example, see post #20 in this thread:
http://www.vintage-radio.net/forum/s...d.php?t=140359.
But there was little or no take-up by the tuner and TV set makers. I suspect that the cost-benefit analyses did not stack up. Also, the VHF TV tuner cascode valves, such as the 6BQ7 and 6BK7, had been developed specifically for this application, so one could say that they were also specialized valves keenly tailored to both the performance and economic needs.
The subsequent VHF TV RF amplifier developments included improved cascode valves, specialized triodes for use in “neutrode” circuits, guided-grid triodes, tetrodes and Nuvistor triodes. Whilst the Nuvistor was developed with a wide range of applications in mind, the other triodes were specialized TV valves, presumably developed with the performance/cost trade-off curve very much in mind.
The VHF TV triode-pentode oscillator-mixer valves were similarly purpose-designed. Although acknowledging the general superiority of the triode at VHF, the industry opted for the pentode mixer as a simple way (in a mass-production context) to avoid the regeneration problem that was consequent to the moving of Ifs right up to the bottom edge of Band I/low band.
TV tuners were of course a blend of cost-conscious mass-production and performance-conscious precision production techniques. It could be argued that in the 1950s, they were doing better at upper VHF and upper UHF frequencies than some commercial communications equipment – e.g. see post #26 here:
http://www.vintage-radio.net/forum/s...=141387&page=2.
Cheers,