One of the most misunderstood (and misused) ideas is that of a wicketkeeper-batsman. Initially, we had seen Romesh open the innings for Sri Lanka, but he was merely a pinch-hitter and not a genuine opening batsman, and his wicketkeeping was top stuff.
But what really set the trend was the entry of Adam Gilchrist. Not only was he a superior wicketkeeper, his blistering (and often successful) batting changed the course of many a match. Gilchrist was a key component of one of the most successful teams of all time, the Australian team of that time and today. While we all remember him for his batting, he was also very reliable and very productive behind the stumps. Fans of every team wished they had him in their teams.
That set off a very negative trend, as all teams tried to find their own answer to Adam Gilchrist. Wicketkeepers were promoted to open at nearly all levels of the game in each country, while batsmen were asked to keep wickets. Alec Stewart and Kumar Sangakkara are well-known examples, but they've been doing it for years. An experiment that failed was that of having Rahul Dravid behind the stumps in the Indian side, only in ODI's. We've seen several genuine wicketkeepers lose their places because of this wild goose chase done by every national team's selection committee. Not surprisingly, we've also seen a large number of 270+ totals, and even more than a few over 300 these days.