I'm sorry, but what's the difference between DPI and PPI? Is it just 'dots' (print) versus 'pixels' (displays)?
As for T221 - sure, we had technology 10 years ago, but that isn't really important - there's a quote in this article, that there are similar displays available today - but for thousands and thousands of dollars, not in device that costs $500. T221 was $18k when it was introduced - if there are no ~$500 displays with similar PPI, it might as well don't exist, since there will be maybe fifteen people in the world that will buy it, as opposed to 3 million people that bought new iPad during weekend.
As for T221 - sure, we had technology 10 years ago, but that isn't really important - there's a quote in this article, that there are similar displays available today - but for thousands and thousands of dollars, not in device that costs $500. T221 was $18k when it was introduced - if there are no ~$500 displays with similar PPI, it might as well don't exist, since there will be maybe fifteen people in the world that will buy it, as opposed to 3 million people that bought new iPad during weekend.