I find myself in somehow disturbed when visiting some (big) online casinos and there is hundreds and hundreds of slot games.. presented just like that ..
This is not resembling in anyway the slot machines in a (real) casino !
The only reason here is that many online casinos get bigger profit in such games that only depends by chance and not with any strategies that can be applied. Slots are just the same as on both offline physical slot games and on online ones, it's just a matter of media simulation. Hence, most still adopts such games as it gives bigger satisfaction to customers and clients on both offline and online slot-supported casinos.
The biggest variations in slot machines is just the layout, some people prefer furuturistic layouts, others prefer ancient looking ones. But there are other differences too, for example there are usually bigger friendly slot where the minimum bet is fairly low. Also when you get a free starting balance in a casino it's usually just for a few favourite slot games. In the end it's just best to try to various games and choose the ones you like.
I don't think the layouts matter in most gamblers. Whatever it looks as long as the animations and the sounds resembles to the physical ones.