I don't have my book in front of me, but I seem to recall looking at the druid summon powers and seeing that they're mechanically very similar to these. The low-level summons require standard actions in order to make the creature attack, but higher-level summons require minor actions. I thought that was pretty good, considering that at higher levels, one might expect that the summoner would get better at controlling the creatures. I expect them to have a scaling economy of actions for the wizard summons as well.
Also, the action trade-off seems fair, considering that what you're doing is trading a one-shot attack for an ability to keep an extra attacker on the board, to soak up damage, dish it out, make OAs, and perform other functions like flanking and blocking. So the choice is between smacking the enemy once, probably with an area attack, or smacking it multiple times over multiple rounds, in exchange for your actions. These seem like good "last fight of the day" dailies. Once you fire off your encounter powers at the bad guys, throw up a summoned creature and bust some heads instead of falling back on your at-will powers.
Or, at higher levels, when attacking with the creature is a minor action, you could do both.
