There is no doubt that scale plays a significant role in the effects of a given ice accretion, but the question that really needs to be asked in these cases is not whether you need the wing anti-ice or not, but rather, when in icing conditions, "What are you doing to maintain the aerodynamic margins that the manufacturer certificated?"
Boeing has avoided ice protection on the tail because they can demonstrate, in actual flight testing and in simulations, that the stabilizer stall margins required for certification are preserved with a three inch ice shape glued to it. This has not been possible to demonstrate in the case of the main wing. hence, TAI is applied to various portions of the main wing on various models.
Generally speaking, Boeing will tell you to operate the wing TAI when ice is detected on window frames, wiper arms or, in the case of the 707, wiper bolts. The "primary" method that they cite is to use it as a de-icer, as they have expressed concern about runback icing if the TAI is not running at a fully evaporative temperature. The exception to this is the 727, due to the pod engines; in this case, they want the TAI run in the anti-ice mode. The 707 also requires the system be operated in the anti-ice mode during approach and landing.
Wiper bolt ice can be extremely hard to see, particularly at night. As I believe I have posted in other threads, there can be situations in which the wing has accumulated significant ice before anything shows up on the bolt. With respect to the de-ice mode, the glaring problem that Boeing has left unanswered is how to decide when to cycle to system the second time...since you can't see the wings, and the ice on the wiper is still there from the first time.
The 707 and 727 required a ten knot speed additive to Vref when ice was on the airframe. I believe you'll find that most, if not all, Boeings require significant penalties to both approach-climb and landing-climb weights when icing conditions have been encountered and the surface temp is 8C or less.
At the end of the day, the goal is to preserve the certification margins. That's pretty much what the pax think they're paying for...those that think, anyway.