Its kind of Funny you bring up that kind of Salamander, how fitting it looks as a basis for the Xenomorph, they can even Regenerate so how fitting.
But ALAS i doubt this was even a consideration when they was designing the Xenomorph.
The Dorsal Tubes were there because they was part of HR Gigers Necronom IV which they decided to use as the Basis for the Monster in ALIEN and so apart from looking very Cool/Alien and carrying over from HR Gigers works, i dont think they had any idea/thought into what role those Tubes had!
When working on the Sequels.... it appears each Team/Director never gave continuation much of a thought! For example, Alien 3 and the Lack of them on the Runner... did they sit down at think WHY does this not have those Dorsal Tubes and thus have a reason WHY those in ALIEN/ALIENS did? I dont think they did at all..
We can Consider Reasons why the Alien in Alien had them, and then look at those in Aliens and look at Environmental Factors and then ask... so WHY did the Camerons Xenomorphs need them?
If we considered they could be used to make a Hive, and Cocoon Victims then we have to ask WHY does the Runner not have them?
Throughout the Franchise it appears they never give such things as far as Continuation much of a thought... and its just about designing something a bit NEW with each release, just for sakes of being a bit different and no more it would seem.
HOPEFULLY... when the Prequels are Done.. we can get another Book that has a in depth and Final Scientific Look at the Xenomorphs in all varieties and give us some explanations.
