Every invention is just a combination of existing things with maybe a new twist somewhere. James Watt wasn't the first person to build a steam engine, he just introduced a separate condenser to an existing design.
It's really hard to find a good line of what should constitute a patentable invention. Personally I think that no software should be patentable, ultimately because I don't think that Mathematics should belong to anybody. But I understand that other people see this differently.
I can still build a machine entirely from off-the shelf parts, connecting them exactly in the ways they're built to connect to each other, and claim to have invented it.
It's really hard to find a good line of what should constitute a patentable invention. Personally I think that no software should be patentable, ultimately because I don't think that Mathematics should belong to anybody. But I understand that other people see this differently.