Sorry for the long build-up in this answer, but I hope that the explanation at the end makes sense and is acceptable by the community.
In T:Salvation, the only way that SkyNet comes into existence is because Cyber Research Systems from T3 creates it from the research done by Cyberdyne. Think about this: Cyberdyne failed to create SkyNet because of Sarah and John Connor's interference. Killing Kyle Reese and preventing John from being born also means that Myles Dyson lives, Cyberdyne research does not get destroyed, and the T1 version (Cyberdyne) of SkyNet is created instead of the T3 Version (CRS).
The major differences that I am aware of between a Cyberdyne SkyNet and a CRS SkyNet are that Cyberdyne launches SkyNet on computer technology based in the mid to late 90's, where CRS Launches SkyNet as a distributed super cluster (it utilizes every computer in the world looking for the virus). Another difference is the types of computer architecture that was available at the time. Multi-core processors were still nearly a decade away in the late 90's and the processing speeds of even high end consumer chips at the time were still way under 1GHz (The Pentium II was available in May of 1997 - just before the original JDay, with a top clock speed of 266 MHz (Pentium II Reference). By the time JDay in T3 comes around high end consumer chips are now right around 2.6 Ghz (Pentium 4 Reference). This correlates to a 10 fold increase in computing power. --I am using Intel chips as processor reference points because they had an overwhelming market share at the time.
It is not clear how much SkyNet knows of it's own history, but it's plausible that it knows the highlights - Dyson starts research, but is killed when the Connors attempt to stop the development of SkyNet. CRS Takes over developing something more advanced. Logically, anyone would be able to figure out that without CRS, a Cyberdyne SkyNet would be inferior.
It's given to us in the films that a CRS SkyNet is much more advanced than the Cyberdyne SkyNet. If you look closely, you see hints that there is time travel already going on. The T800 series has already been developed by SkyNet in 2018. Kyle Reese, in the first movie, said that the 800's were a new model when he came back from 2029. This means that SkyNet either was able to develop this model 11 years faster because it was already more advanced, or SkyNet from 2029 sent a lot of intelligence back in time to alter the early war around the same moment it was sending the first T800 back to 1984.
Another hint that there is time travel is that SkyNet tells Marcus Wright about past attempts to assassinate John Connor. There is an allusion to sending machines to kill him in the distant past but they were unsuccessful because they weren't human. SkyNet's knowledge of these past events can only come from future knowledge sent back by means of time travel.
When you take into account that there could have been intelligence sharing from the future, SkyNet should reason that John and Sarah Connor were responsible for it's advanced development by forcing it to be developed later, and launched into a world with vastly more powerful computer systems. At this time, SkyNet actually depends on John and Sarah Connor in the 90's as key contributors to it's development and therefore are critical to it's existence. For this to happen, Kyle Reese must live and be sent back to Sarah in 1984. However, Future John Connor is no longer an asset, but instead a threat, he must be eliminated. Kyle remains bait until John can be terminated, and then when the time displacement equipment becomes available - SkyNet would send Kyle back to 1984.