28-300L superzoom vs 24-105L + 70-300L ?

I was wondering about the price/performance ratio of this 10x superzoom 28-300L and saw that, according to the image quality graphs on the-digital-picture.com this lens is behind the 24-105L and 70-300L together and the price is higher than the other lenses together.

What people really do decide to buy this superzoom ? I can only guess as it is an all-around-travel zoom. Just like a 10x P&S camera with an SLR taste.
The reason I post this ? Just curious.

I just bought the 28-300L and 70-200/2.8 II on Friday.  The camera shop offered me big discount  of buying these two lens.  I like to take portrait using the tripod and want a wide angle to medium telephoto lens equipped with a tripod collar.  This helps me change from horizontal to vertical easily.  28-300L seems to be the only choice on market which meet my requirement.  I did not have much expectation on the 28-300L due to this is a high power zoom and the IQ should not be so good, at least I thought it cannot compare with 70-200 II.  I tested these 2 lens during the weekend.  I am surprised to find that the 300mm IQ of this lens is so nice.  The IQ is closed to my 400/2.8 IS II.  70-200 II + 1.4 III cannot compare with 28-300L.  The focus speed of 28-300L is also very fast.  The IQ from 28 to 70mm is not as good as my 24-70/2.8L II but the difference is not that big until I crop to 100%.  Tonight I will post some comparision photos.

The problem of this lens is the IS and the heavy weight.  I cannot obtain a good result when handheld.  When I point down it will slide to 300mm.  If there was a lock it will be better.  This lens also cannot accept extender.  The price of this lens is similar to 70-200 II.  I prefer this lens to 70-200 II.

First of all this lens wasn't launched as a consumer lens. I know the average consumer likes to have a long zoom just like you said (bridge cameras for example offer just that). This lens was launched in 2004 when few consumers had even a dslr and an even smaller proportion of those we're using full-frame. Also the launching price was 2500$ which is very expensive even today for the average consumer.

The lens was geared towards photo reporters (especially those working for newspapers that didn't need the best IQ available) working during daylight. For a photo reporter getting the picture is much more important than IQ and a 28-300 range will increase the chances of getting the picture much more than using a prime or a shorter zoom.