90% of the questions asked in the Topics here can be found with a small amount of "googling" etc, and there are a good few sites like the one you mention that help with advert tunes
But some people are "lazy" and would like to just ask the question...go get a cup of tea, walk the dog etc, and come back and find their answer waiting for them. Even if the same question has just been asked and replied to on here, the question will still get asked.
That site is pretty useful, yes, but I do sometimes find it a bit slow in being updated. As most questions in the advert section relate to music from current or very recent ads, it's always possible that the site won't have it yet. Certainly well worth a look though.
That said, I don't see what's wrong with asking on here (apart from when questions get repeated for the 1000th time). Sometimes it's nice to get an answer from a human, even if it is just on a web forum. :-)