Why do some cheap beers taste sweet? I had a Tui (cheap New Zealand pale lager) the other day, and it tasted sweet!

Why is this? Is possible that sugar is added during the brewing? What else would make it taste sweet?
The alcohol in beer is created as a byproduct of the yeast consuming the sugar in wort during the fermentation process.  For a beer to taste sweet, there are two possibilities:


The yeast died before the fermentation process ran to completion.  There are various chemicals that can do this.
The wort contained some non-fermentable sugars.  If the yeast can't feed on a particular type of sugar, then it is going to remain in the end product.  Lactose is a traditional example of such a sugar but some artificial sweeteners have a similar effect.


Assuming that the flavour was intended, I would guess that this was (2): using non-fermentable sugars allows the brewer to know exactly how much will end up in the final beer.  It is also the only option if they do in-bottle carbonation, since that requires live yeast in the bottle.