I think the odds were best in Civ3, actually, and they were surprisingly good - like one in seven or something, if the spearman has terrain and fortification on his side.
Actually in 2, the odds could be as high as 1 in 3.
Spearman vs tank had been a big problem in civ1. In-game occurences of such things were frequent. The most powerful units were often defeated by militia or chariots or even workers. Civ2 attempted a fix by introducing hp and combat with multiple rounds. Under regular circumstances, a spearman now had to beat a tank consistently over a number of rounds of combat, so in-game occurences dropped drastically and have remained low ever since. However ... under specific circumstances (elite ie 5 hp spearman, in a walled city, on a hill vs 1 hp tank) the odds went way up, to as high as 1 in 3, because the spearman now had 5 chances to beat the tank.
Civ3 and 4 both introduced measures to drop the odds under these specific circumstances, and the odds have consistently dropped with every version of the game. 1 was worse than 2 was worse than 3 was worse than 4. But it's not until 3 that people really started to get up in arms about it.
The fan base was alot different in civ1 and civ2. This sort of thing was taken in stride, because computer strategy games were shiny and new. Many of the players were very used to incredibly complex but very realistic combat systems in war games, and they were tired of them. They weren't looking for that in civ. A bit of abstraction was taken in stride; civ had light, simple rules and its sometimes odd abstractions were forgiven, on two accounts. One, it was a computer game so you could play it alone. Two, it covered all of history instead of a single campaign, so some stretches were expected. Basically there was a lower bar for suspension of disbelief.
The spear vs tank thing really got people howling when civ3 arrived, though, because the novelty of computer games had pretty much worn off, and there were lots of games with good combat models. Also, the wargames industry had died (and Civilization itself played no small role - it was the lawsuit over the name that killed Avalon Hill) so people turned their attention to computer games for realistic strategy games. Civ3 had to deal with different expectations.