Like always on stack exchange, the accepted answer is not the best one. The other answers are better in that they explain that our numeral system has a differen

Like always on stack exchange, the accepted answer is not the best one. The other answers are better in that they explain that our numeral system has a different origin and development from our alphabet. Not all languages have two cases for their script, it's really as simple as that. Oldstyle numerals versus lining is mainly a typographic distinction rather than anything as meaningful as the usage of case in English for nouns and acronyms. (it's similar to small caps vs regular ones)