Well, not entirely. "Runaway Bride," "Voyage of the Damned," "Next Doctor," "End of Time," and "The Doctor, The Widow and The Wardrobe," feature a guest character as the main companion.
Meanwhile, "The Christmas Invasion," "The Snowmen," "The Time of the Doctor" and "Last Christmas," still prominently feature the main companion. "A Christmas Carol" focuses more on The Doctor and the old man, but Amy and Rory are still very much present and active throughout the plot, so make of it what you will.
It's almost half-half really.