I have often been frustrated with the difficulty in attacking prior to tanks, but the more I have thought about it, I think that the CIV III system is actually pretty realistic for WWI era battles. Yes, infantry attacked as often as it defended, but the general rule in military planning (even to this day) is that to attack, you should have 3-1 superiority at the point of attack. Infantry will usually lose to infantry, as it should, but three infantry will usually beat one, especially with artillery prep. This is where the value of armies comes in (Although I think they are too expensive), three infantry in an army can usually take out the best defender, then recover. Three individual infantry can still win, but you will lose one or two in the process.
If you look at the history, post-Napoleon, most battles against entrenched infantry were slaughters for the attackers. Napoleon was still able to use cavalry to outflank his opponents, or mass infantry for a charge, but they were still predominantly musket infantry at that point.
During the Civil War, (which would equate to Riflemen, IMHO), Cavalry was best used for scouting or raiding (pillaging), or occasional attacks against scattered detachments (conscripts?). Forrest, Stuart, even Sheridan did not make there reputation assaulting defended cities. In fact, fortified cities such as Vicksburg or Richmond were able to withstand sieges for years, and only fell when on the brink of starvation after constant bombardment and isolation. (And yes, their populations were reduced in the process, and many improvements destroyed.) Most other major battles involved infantry vs. infantry, and the defense always had an advantage, unless one side's morale could be broken. This is harder to simulate, but I look at elite/veteran/regular/conscript as a parallel to this. An elite riflemen could beat a conscript one on one, three of them for sure could.
The next major wars were the Austro-Prussian war of 1866 and the Franco-Prussian war of 1870. At first glance, this would seem to defeat my premise, since the Prussians were able to defeat their oponents in one decisive battle. However, there is more involved than that. Having just finished a paper on the Franco-Prussian war for Command & General Staff College, I was suprised to learn that the new improved rifles of the Prussians (the "Needle Gun" first used at Konigsgratz) were not as decisive a factor as popularily believed. There were a number of other factors involved, including concentrating more troops on the battlefield quicker, and the improved quality of training for the Prussian conscript troops. However, one of the biggest factors vs. the French was the superior rifled artillery, vs the French who were still using older field pieces. In game terms, they both had Infantry, but the Prussians had Artillery, while the French had cannons. After sufficient bombardment, the French morale was at the breaking point (1HP), and the Prussian infantry was able to overwhelm them.
WWI showed all powers with fairly equivalent infantry and artillery initially. The Germans made impressive gains early due to suprise, better mobilization, and out-maneuvering the allies, but once the fronts streched out so there were no more flanks to take, it bogged down to the trench warfare we all know. The only way to advance was to mass a huge force in a small area, pummel it with bombardment, and then rush "over the top". After a short gain, however, reserves would fill the gaps and the offensive would bog down. That is what Infantry warfare in Civ3 can get to. Towns are expensive to attack without huge bombardments, then the infantry pounds away with big losses. Armies can help to some extent, because the first two units can recover, and are not totally lost. This drove the invention of the early tanks, and planes, as ways to overcome the trenches. In fact, however, this new technology was not as decisive as the fact the Germans reached economic and manpower exhaustion, while the Allies were boosted by the fresh troops and factorys of the Americans.
Sorry, this turned into way more than I wanted to, but I do believe that the current system is pretty realistic, even if it is frustrating. Infantry combat heavily favors the defensive, unless the enemy makes some dumb mistakes (like the AI does), but it is possible if you are willing to mass and overwhelm the enemy, with heavy bombardment. There were at times heavy infantry or other formations that were designated for assaults (Napoleon's Guards, the German Stormtroopers, etc), but rather than showing new units, I see those as being the Elite units already in the game.
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