After looking at history of technology there seems to be no major changes. were there small improvements that had a big impact or is there another reason all together?
This is a tricky question as the conflicts are not really comparable. One answer is that the sheer scale of WW1 forced constant (if individually small) rapid advances in medicine (such as treatments for specific injuries) and logistics (such as casualty clearance procedures and medical supply), with enormous numbers of test subjects available (the casualties) and huge national resources devoted to the field.
Compare the survival rate of British military personnel suffering a broken femur between the outbreak and the end of WW1, for example. At the outset of the war, the fatality rate was in the region of 80%: medical staff struggled to deal with both the injury itself and subsequent infections, and it was extremely difficult to move the patient without inflicting potentially fatal pain shock. By the end of the war the overwhelming majority of men treated for such an injury survived, thanks to improvements in treatment techniques and the development of specialised equipment (specifically the 'Thomas' splint, in itself a fairly simple device, which both aided treatment and made it safer to evacuate the casualty back to the UK).
But as I say, the Boer War and WW1 are not directly comparable conflicts and so raw statistics can be misleading. When we think of WW1 from the British perspective, we think mostly of the Western Front, and in this theatre a casualty could be undergoing treatment from an experienced surgeon within hours, and could be in an English hospital (such as Netley, on the south coast) within days. By mid-war, here's how a casualty could expect to be evacuated after being wounded on the line:
The wounded soldier’s first treatment was most likely to be provided by himself or his immediate comrades using their Field Dressings (two bandages and safety pins). Frequently rags, jerseys, puttees and so on would be adapted to fill larger wounds and to help make the patient comfortable. There were no pain killers available, although some officers carried their own private supplies of morphia and there would sometimes be a certain amount of rum around.
Each battalion had a Medical Officer with a staff of regimental stretcher bearers. A Regimental Aid Post (RAP) was established in the front line, usually in a dugout: cramped, dirty and smelly, the doctor working by the light of flickering candles, discarded bloody dressings and soiled uniforms and kit thrown aside, the treatment taking place on a stretcher or cot.
Cases needing immediate treatment would be taken to the RAP, while less severe cases would be carried or directed to make their way to a Collecting Post set up by a Field Ambulance unit just behind the lines, perhaps a farm building or the cellars of buildings in a ruined village where further hasty treatment would be possible, still within artillery range.
From here ambulances or carts would transfer those unable to walk themselves on to the Advanced Dressing Station (ADS), perhaps a mile or so back from the Collecting Posts but still within range of the guns. Here there would be more shelter, from both weather and shelling, for stretcher cases awaiting dressing or operations or just waiting their turn for an ambulance.
Behind the ADS came the Main Dressing Station where treatment could be carried out in relative comfort. Then came the Casualty Clearing Station (CCS), large tented or hutted camps where several surgical teams carried out a wide range of operations and care was provided in the wards before onward transmission of the patient by Ambulance Train to a Base Hospital, and then for more severe cases by Hospital Ship to England.
This sort of treatment was possible at the time only because the front line was relatively fixed, and because the theatre of conflict was so close to home. Compare this to South Africa, where the fighting was far more mobile, the distances to surgical aid and hospitals (where available) far greater, and the only way home a multi-week voyage by sea; all of these factors would severely impact casualty survival rate and the nature of wound treatment. There were a great many cases on the Western Front where the system was overwhelmed by casualty numbers, or where individual casualties couldn't be recovered due to shelling or other enemy action, but your chances of timely surgical treatment were far greater compared to Africa. It's difficult to extrapolate, therefore, how qualitatively better medical treatment had become between the two conflicts.
A clearer picture might emerge if you compare combat casualty survival rates from British troops fighting in East Africa during WW1 with their Boer War counterparts, but I don't have a source for these statistics. Those statistics might be muddied, though, by the impact of tropical diseases on already wounded men.