Your argument, that GPL was KHTML's only advantage, doesn't make any sense because it then follows that Apple chose KHTML because they just love GPL and won't accept anything else despite KHTML's supposed technical inferiority. In other words, you're saying Apple chose KHTML because their only concern was apparently to get to be forced by GPL to release improvements. Because if KHTML was so inferior and forced them to release improvements (let's imply Apple didn't like this), what reason would they possibly have to choose KHTML? "Oh, look, there are these other engines which are better than KHTML but unfortunately their licenses don't force us to release our work, so no, we choose GPL."
In reality KHTML was a much better code base than other options, and Apple didn't really care that much about the license.
Let me tie in this comment with the whole thing about GPL vs. non-copyleft free software drama in general, and why I think GPL has become harmful: what you said I think illustrates a kind of thinking mode that the idea, the practical working principle, behind GPL breeds. The idea is to use force and coercion to make entities do what you want them to do. That road naturally leads to a mindset where every behavior is seen as necessarily motivated by coercion. And that leads one to normalize and accept coercion as an acceptable, even necessary, mode of social relations. I see this mode of thinking a lot with strong advocates of GPL. It's always in terms of someone being forced to do something good, and if they aren't being forced no good shall come out. This is a horrible, horrible way to look at the world. If we take Apple as an example, they open-sourced a lot of stuff they had no legal reason to release, some of those things very non trivial.
I have to point out that I'm writing all of this as someone who respects RMS and FSF's cause a great deal, I even use the term free software rather than open source (in my native language, fortunately, there's no confusion about "free", free as in freedom and free as in bear are not homonyms). However, I do not think GPL and strong copyleft licenses are an acceptable, or even a good way, to accomplish freedom in this domain of life. GPL is maybe a great tool to destroy proprietary software (well, almost, but not quite), but a horrible way to accomplish software freedoms in general.
relying on the goodwill of an entity will almost always get you nowhere. Apple (or any other major corporation) does what they do purely for profit - and of their decision to unilaterally release source code (without coersion from a license) is made based on the positive PR gains, on the fact that releasing software to commoditize the competition will help their own business, or for some other publically unknown reason.
It's always better to encode, into law, ethical behaviour we want, instead of hoping for it from people. Doubly so when the 'person' is a corporation.
In reality KHTML was a much better code base than other options, and Apple didn't really care that much about the license.
Let me tie in this comment with the whole thing about GPL vs. non-copyleft free software drama in general, and why I think GPL has become harmful: what you said I think illustrates a kind of thinking mode that the idea, the practical working principle, behind GPL breeds. The idea is to use force and coercion to make entities do what you want them to do. That road naturally leads to a mindset where every behavior is seen as necessarily motivated by coercion. And that leads one to normalize and accept coercion as an acceptable, even necessary, mode of social relations. I see this mode of thinking a lot with strong advocates of GPL. It's always in terms of someone being forced to do something good, and if they aren't being forced no good shall come out. This is a horrible, horrible way to look at the world. If we take Apple as an example, they open-sourced a lot of stuff they had no legal reason to release, some of those things very non trivial.
I have to point out that I'm writing all of this as someone who respects RMS and FSF's cause a great deal, I even use the term free software rather than open source (in my native language, fortunately, there's no confusion about "free", free as in freedom and free as in bear are not homonyms). However, I do not think GPL and strong copyleft licenses are an acceptable, or even a good way, to accomplish freedom in this domain of life. GPL is maybe a great tool to destroy proprietary software (well, almost, but not quite), but a horrible way to accomplish software freedoms in general.