I'm not convinced any unit lacks coil whine. I think some people are just more sensitive to it. If i put my ear to the back of the tablet portion while it's charging I can hear it plain as day, but the unit is dead silent to me under normal operation.
So I guess the question is, am I just not sensitive to it, or is the coil whine so bad on some units and mine just isn't bad? Kinda hard to judge when I haven't heard a sampling of someone with a "bad" unit to compare to.
I'm just kinda curious, I've seen a lot of complaints about it, and I think I'm missing something.
I don't have another 13.5-inch model to check out either. All I can say is that on mine, it's loud enough that I can hear it even when there's some background noise. If I'm in a very quiet space, then it's incredibly obnoxious. The 15-inch models I've used both have it like you describe -- you can hear it when you hold your ear to the tablet, but otherwise it's not audible.
So I'm going by the 13.5-inch versus the 15-inch to say it can be really bad on the smaller one, which correlates with what I've seen in my research. I'm pretty certain that it's a range with all machines, from barely audible to obnoxious, with the 13.5-inch machines for whatever reason representing the worst end of the range.