There was a debate going on in the mid-19th century about whether the new rifled weapons had made cavalry obsolete. The new theories were that cavalry could no longer charge infantry due to the increased range of the infantry weapons. Hence a lot of early war generals did not train their troops in the use of the sabre and instead picked up the carbine for dismounted fighting. Few early war troops were really capable of mounting sabre charges because it requires a much higher level of training. Some of the very early cavalry regiments in the East (i.e. those that were with McClellan's army in the autumn-winter of 1861) were so trained, but those that joined after never really were.
McClellan's cavalry made a few sabre charges on the Peninsula, but not at much more than squadron strength (he had very little cavalry, the vast majority of his available cavalry was held back by Lincoln), and famously charged at the small Battle of Boonsboro on the 15th Sept '62. However, Hooker's "Cavalry Corps" meant a doctrinal change away from charging, towards dismounted action. This suited the Confederates as they carried infantry muskets instead of carbines and proceeded to shoot the Federals to pieces.
The major change came when Sheridan took over. The cavalry of the Army of the Cumberland was some of the best the Federals had, and because one of the brigadiers, Minty, was a ex-British soldier he knew a lot of the American bluster about the inability to charge the new weapons was just due to a lack of drill, and so trained the "Saber Brigade" to deliver shock charges against infantry. Under Sheridan the cavalry eventually made successful shock charges against entrenched infantry in 1865 (see Five Forks).
At Gettysburg the ability to charge was essentially about the confidence of the commander. Perhaps the game has it right, as Buford was a "dragoon" type who didn't believe in shock tactics.
One should note that Buford was in fact not seriously engaged at Gettysburg. His casualty counts are, by tactical regiment*:
8th Illinois: 7 out of 567
combined 12th Illinois/ 3rd Indiana: 52 out of 675
8th New York: 40 out of 707
combined 6th and 9th New York: 23 out of 731
combined 17th Pennsylvania/ 1st Sqn, 3rd West Virginia: 8 out of 528
* understrength regiments were combined into single tactical regiments, but remained separate on paper.