And why would Arabic numerals count by that logic? That's not native to Japanese either. The 5dIV is called the "five dee mark four" which in Japanese would contain the word. Other Japanese companies don't seem to avoid the number too much. Nikon had a D4 and a J4. Sony had a PS4. Fuji has an XT4.
In any case, number 4 can be pronounced as both shi or yon in Japanese. The latter seemingly preferred due to the death connotation of the former. But for the same reason, the use of the number doesn't seem to be avoided by Japanese companies to the same degree as Chinese companies.