1. DVI has supported higher resolution displays for a long time; 1920x1200 since 1999 on single-link, and 2560x1500 on dual-link. Note that this is more than '10 years ago'.
2. HDMI has supported 4K displays since May 2009.
Most of your post belies a misunderstanding or underestimation of the technology involved. The bottleneck was never 'content protection filters' so much as the feasibility of building electronics that can handle higher-bandwidth signals over cables with no extra data channels (in a backwards-compatible manner), and the challenge of getting manufacturers to make hardware that would actually support it, at increased cost, for no practical benefit.
For older LCDs, it was an issue of new technology is expensive. I remember when everyone I knew had 15" CRT monitors, and having a 15" LCD monitor was a luxury that almost no one could afford. It might be hard to remember, but consumer LCD displays were new once, and new technology is never cheap. On top of that, the cost of an LCD panel doesn't scale linearly with diagonal size, so going from 15" to 17" to 19" was a huge cost curve. Until LCD production was more consistent and people understood the point in buying them over CRTs, the market didn't really heat up, and so sizes/resolutions never grew.
As for DPI, LCD DPIs depend on the size of pixels, which are a mechanical element. In contrast, CRT displays are a printed screen of phosphors; paint a smaller, more detailed phosphor grid, adjust the electronics for more precision control, and boom, higher DPI.
1. DVI has supported higher resolution displays for a long time; 1920x1200 since 1999 on single-link, and 2560x1500 on dual-link. Note that this is more than '10 years ago'.
2. HDMI has supported 4K displays since May 2009.
Most of your post belies a misunderstanding or underestimation of the technology involved. The bottleneck was never 'content protection filters' so much as the feasibility of building electronics that can handle higher-bandwidth signals over cables with no extra data channels (in a backwards-compatible manner), and the challenge of getting manufacturers to make hardware that would actually support it, at increased cost, for no practical benefit.
For older LCDs, it was an issue of new technology is expensive. I remember when everyone I knew had 15" CRT monitors, and having a 15" LCD monitor was a luxury that almost no one could afford. It might be hard to remember, but consumer LCD displays were new once, and new technology is never cheap. On top of that, the cost of an LCD panel doesn't scale linearly with diagonal size, so going from 15" to 17" to 19" was a huge cost curve. Until LCD production was more consistent and people understood the point in buying them over CRTs, the market didn't really heat up, and so sizes/resolutions never grew.
As for DPI, LCD DPIs depend on the size of pixels, which are a mechanical element. In contrast, CRT displays are a printed screen of phosphors; paint a smaller, more detailed phosphor grid, adjust the electronics for more precision control, and boom, higher DPI.