TV repair has become obsolete because:
1. TV quality/features are changing more rapidly
2. They are cheaper relative to average income than ever before
3. The labor cost/repair vs. buying new with "insurance" is not worth fixing
Many people these days are just picking up "insurance" which lets them swap their defective TV for a new one within the first 4-5 years. After that, they will likely toss it and buy a new one because the economics are not worth it. Factor in the repair cost and time without a TV, and the fact that a new one will come again with a 4-5 year warranty/"insurance", and has enough new features to make it worth the switch... It's a hard sell.
More and more TV repair these days is done by electronics do-it-yourselfers like folks here on the EEVBlog who learn about it and want to test their skills first, knowing if they don't success they'll toss it and buy new one anyways. Combine that with shops online like
http://www.shopjimmy.com/ that sell you "component kits" to full boards of commonly failed parts on many TV models, and if you can usually fix things yourself.
There are the simple blown-cap type jobs on power supplies which you can buy components for yourself, to more complex multi-part failures that take a bit more time
(see for example 3:50 in the video below):
Nevertheless, the AVERAGE person will go to BestBuy and pay $100 non-refundable "diagnostic fee". Then once you add labor and cost of parts.... Say a board costs $50-100, and then another $50 labour, you are at least in the $200-300 range with taxes in. Doesn't matter whether TV is 36" or 50". Even if the board is 99% good and 1 cap is blown, the tech will likely replace entire board and NOT replace single caps by de-soldering/re-soldering. Then they give you 90 days warranty.
Meanwhile, you'll find these new 50" TV's for $500-600. They give you maybe 2 year manufacturer warranty, then you pay another $50-100 for maybe to cover you for years 3-5 (or whatever it is).
I think it is purely economics. Even if TV features don't change much, the ratio of cost of repair to buy new is tipping the decision of most average consumers, while electronics hobbyists do it because (A) their labour is "free" and for the most part they consider it a challenge to see if they can fix it, and (B) most will have at least some gear (soldering iron, meters, scopes, component availability), and (C) they know the cost of components is miniscule and it is worth spending the time to fix it.