You can just as well pronounce those and it'll still be valid Russian. It's just that they are commonly omitted, but there's no rule mandating it.
Well technically English has no rules mandating anything, since there is no central institute or authority for the language. Doesn't mean there aren't effectively rules.
Practically, rules that people 50 years ago would never break are routinely ignored now, there are a bunch of things that are grammatically correct but you wouldn't ever say, etc... If something is done one way practically all the time, it might as well be a "rule", whether it officially is or not. Makes no difference to the person who has to learn it.
But that doesn't mean that the rules for English orthography aren't insane. There are very few English sentences that can be read by sounding out letter after letter individually (no matter what sound you choose as the basis for each letter.)
Well technically English has no rules mandating anything, since there is no central institute or authority for the language. Doesn't mean there aren't effectively rules.
Practically, rules that people 50 years ago would never break are routinely ignored now, there are a bunch of things that are grammatically correct but you wouldn't ever say, etc... If something is done one way practically all the time, it might as well be a "rule", whether it officially is or not. Makes no difference to the person who has to learn it.