ばか！バカ！　馬鹿ー月！

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Back in medieval Europe prior to 1000AD, where the only people using the progenitor of today's Gregorian Calendar live, they were probably reading their years like this:

525: Five Hundred and Twenty-fifth (year of our Lord/ Anno Domini) (First year where they use "birth of Jesus" to count their years, before that they used Foundation of Rome)

656: Six Hundred and Fifty-six(th year of our Lord)
796: Seven Hundred and Ninety-six(th year of our Lord)
999: Nine Hundred and Ninety-nin(th year of our Lord)

And after 1000:
1000: One thousand(th year of our Lord)

So even in 1010, people were reading it as One thousand and tenth year of our Lord.

I think it was only around after 1500 that people began splitting the numbers into two segments to make it faster to pronounce, though you'll still see in those 19th century and before stone tablets in historical buildings as well as documents with the years still read out in full, like in the Declaration of Independence:

"In the Year of our Lord, One Thousand Seven Hundred and Seventy-Six"

Even in some legal documents today, when written in full, the year is completely read in full, so years like 1995 became "One Thousand Nine Hundred and Ninety Five".

Though as the years between 2000-2009, it was more convenient to pronounce "Two Thousand" to "Two Thousand and Nine", the discrepancies in these legal documents became less pronounced.

Logically, 2000-2009 should be pronounced "Twenty-Hundred" to "Twenty-oh-Nine", but humans are lazy.

Interestingly, in Japanese, the years are all read out in full. So back in the 20th century, years like 1997 became "Sen Kyuu-hyaku Kyuujuu-kyuu nen". Which was a mouthful, this is why they kept Emperor's era names. So instead of using "Sen Kyuu-hyaku Kyuujuu-kyuu nen", they can simply use "Heisei Kyuu nen" or "9th year of the Heisei Era" (abbrevaited as Heisei 9).

As of today, 2010 is Heisei 22. Though pronouncing "Ni-sen Juu nen" is less mouthful than the 20th century years at the moment, I think the Japanese will continue to keep their era names for they know the numbers will eventually become cumbersome to pronounce. I think that's the true reason why they keep their Emperors, despite them being constitutionally useless.

For Chinese, no such problem exist, as the years are simply read digit by digit, so 2010 is "Two-Oh-One-Oh".