I wish to give my opinion on a couple of ideas that have been touched on by a other folks in this thread. The first is ma-ai. If the attacker is too far to punch, they may still be close enough to kick. Sometimes we don't think of that while focusing on punches and grabs. This is what many people that train in different fighting arts are taught, particularly in Jeet Kune Do. There is a "kicking range", a "punching range" a "trapping range" (kind of like Tai Chi's Sticky Hands) and a "grappling range" (on the ground). So the point is to be aware of the attackers' distance so we can be prepared for what may be coming.
The second thought that entered my cashew-sized brain is "diversion". Again, in JKD we are taught to either punch with a single direct attack (with the intent to disable with the first blow) or attack with combination (in order to get the defender backing up on their heels). It is not assumed this will always be successful so both of these tactics are usually combined with a kick either first or second to divert the attention of the defender either high or low. Punches to the face area tend to bring the defenders' attention and hands up leaving them susceptible to a low kick. Delivering a low kick diverts the attention low to open up an attack high.
These points strike me as being important to an Aikidoist. We all try to keep a "soft focus" on our partner to be aware of anything, but if we don't occasionally see some kicks headed our way, when it happens we may not be able to act as quickly as necessary because we have not developed the muscle memory required to act without thinking too long.
My 2 copper pennies worth!