This is true to the extent that the model is accurate. The assumption leading to this model is that the rate of absorption is directly proportional to the amount remaining to be absorbed. However, another plausible model is that the rate of absorption is proportional to the surface area of the depot remaining to be absorbed. Real life probably includes a combination of these and other complications. There are assertions in the literature that apparent half-lives do seem to increase with the dose. I commented further on the surface-area model here.
