Symbol for ideal voltage source vs symbol for real voltage source
There are lots of little niggles in wikipedia, such might be expected from a large collaborative amateur effort, this is one of them. 

Ideally, a real voltage source ought to be depicted like this, if the only non-ideality that's being modelled is the internal impedance. It's the principal non-ideality. We tend to ignore noise, drift, strange current limits, and changes in effective Rinternal in favour of this simple model.







simulate this circuit &ndash; Schematic created using CircuitLab

Either that, or the diagram you've picked out ought just to be labelled a plain voltage source. It is now ;-). It's difficult to know what's for the best, without a major overhaul of the article. For instance, what on earth is the PO Box paragraph doing in there? It's unnecessary and insufficient!