It's useful to note here too that UK's work in WWII was started by desperate Polish need, and there is indication they got somewhat further ahead than people tend to credit them for. (It's interesting to wonder if Poland may have been ahead in computation if it wasn't, you know, invaded, and forced to kick the ball over to the UK.)
It's also worth noting the different approaches to "war time secrets" the US and the UK took. Where Alan Turing had a strong practical head start on computation in WWII, his work was locked under confidential and secret designations and he was not allowed to commercialize it after the war. Worse, he was almost entirely stopped from building practical machines, and it's a wonder he managed to contribute as much to computing theory as he did even with the restrictions he was under. (Also don't forget his own government lead him to an early suicide.)
The US in its contractor-based approach (including IBM's involvement) didn't hamstring commercial interests anywhere near as strongly (despite declassified hindsight now telling us they were straggling behind, comparatively, UK's efforts) so much after WWII by locking things into a "classified vault" and the US did not try stopping the people who had worked on computation from continuing to work on computation.
If English had had twice the number of glyphs, IBM would still have existed, even though they'd have had more work to do. There might have been some number of glyphs past which the burden might have slowed progress enough that some other nation would have been competitive, but it's all just information, and ultimately computer engineers would have figured out something.
Or look at some evidence: Japan already had what it needed to communicate digitally before WWII in spite of having a complex script (three, four if you include romaji), and most computer engineering and computer science progress came after WWII, and indeed, Japan's computer industry did reasonably well post-WWII -- comparable to France's, which did quite well considering how much smaller France was than the U.S. in population, industry, wealth, etc. And: need was decidedly critical in the UK's computer engineering and science development during WWII (Alan Turing, Colossus). France, Japan, and the UK, each had some of the conditions that the U.S. also had, but not as many, so it's not surprising that the U.S. did well.
I've a feeling that among the things that helped the U.S. that I didn't list above are also: the decadal census (which is intimately related to IBM's rise), Sears & Roebuck (the antecedent to Amazon), the immense geography of the country and widely dispersed population (which impacted the preceding two items). I bet others can add items to the list. Some of these certainly existed elsewhere.
Of somewhat less importance is that a number of very important mathematicians who helped found computer science (e.g., Claude Shannon, Alonzo Church, Haskell Curry) were Americans. Their research was published, of course, and many others were not Americans (e.g., Charles Babbage) which is why I say they were of less importance.