My question arose from this article on Wikipedia on the GC-skew in bacterial genomes: https://en.wikipedia.org/wiki/GC_skew As far as I understood, the lagging strand (the template strand), during replication, is more often single stranded than the leading strand (template), so it is more prone to mutations like deamination. Therefore, on the lagging strand (here, the one being the template to the strand formed by Okazaki fragments), one should expect more Ts and fewer Cs. Conversely, the strand synthesised by Okazaki fragments should have an enrichment of As and a depletion of Gs. Why does the Wikipedia article mention a increase in the ratio of (G+T)/(C+A)? I would expect an increase in the ratio of (T)/(C). I don't get the link with Gs and As.
I think you are referring to this sentence from your wikipedia link:
There is a richness of guanine over cytosine and thymine over adenine in the leading strand and vice versa for the lagging strand.
Note that this is not saying (G+T) > (C+A). It is instead saying (G)>(C) and (T)>(A). I think that those are not the same as saying (G+T) > (C+A), though that is also true, probably?
So I think that there is no contradiction there- it is just, as you say, more Ts (relative to expected equality with As) and fewer Cs (relative to expected equality with Gs).
If I understand correctly, the importance of the GC skew, and the reason that it is interesting, is that it acts as a deviation from Chargaff's parity rules (as explained in the article). These rules state that for any given hunk of DNA, (G)~(C) and (T)~(A), which is the expected composition for (for example) double-stranded DNA, because of base-pairing.
Edit: for more information on Chargaff's rules, see this other question which I have (through pure coincidence) answered here. Note that the second parity "rule" is a statistical phenomenon, rather than a logically required rule. The wikipedia page on Chargaff's rules is also informative.
Hope that helps.