I believe command stars only affect morale in RTW and M2TW. A CA staffer said here that they affect attack stats as well, but testing by therother apparently refutes that. Like Orda I personally have not noticed a big effect of command stars in those games.

In MTW (and I believe STW), command stars did affect attack (and defence?) stats so an 8-star general could turn weak troops into monsters and be very hard to beat. I found command stars had an enormous effect in MTW, with a high command AI general's force often being able to roll straight over your zero command armies.