But it is not realistic ?
OpenTTD is a game, it is not meant to be realistic.
And second question: when train push goods from oil refinery to station in town-centre - goods not used or very slow used by town citizens.
Is it some limit to goods-used speed in towns ?
Can user increase this limit by use good-carry car in this town ?
I'm not sure what you're asking here. But the same applies to citizens (or towns/cities however you want to word it). They'll accept all you send them. The only limit is how much mail and passengers they will OUTPUT. The output for towns and cities will increase as they grow.
Again, all of this might be changed by a patch or GRF, if you're using them.