My supposition is that this is was more or less an automatic designation based on the fact that Rule 110 requires an infinite "background tiling" of the 14-bit sequence
00010011011111, and since by convention a proper Turing-complete system is supposed to begin with a blank tape or its equivalent, this doesn't count.
I would understand the argument for "weakly" universal if the tiling sequence was dependent on the program in some way, but that's not the case here. In fact, as near as I can tell, within the mathematical universe of Rule 110, that sequence is the blank tape.
(The staggered small triangle tiling is what this sequence looks like on a typical plot.)
If you start with virtually any aperiodic seed row (e.g. a few random bits on top of a
0 tiling), the system invariably settles into a state where the obvious background is that sequence. It's the sequence of least resistance, sort of the lowest-energy vacuum state of the Rule 110 universe. On top of that, it's a constant finite overhead, which already to me seems like suspect grounds for the "weakly" qualifier.
Is there a good reason for this designation that I've missed or something I've misunderstood?