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No, they are not equal, otherwise you could take 600 one second subs and it would be the equivalent of one 10 minute sub. Which of course is not true. Many faint objects will not be there at all in a one second sub, so it doesn't matter how many you take, there is no information there to sum/average/median or otherwise process.
Long subs are needed when there are very few photons around and the sky is nice an light-pollution-free. You need a long exposure to pick up the fainter details.
Now of course the problem is, even under perfect skies that the noise in the camera increases the longer the sub, hence the need to take lots of subs to cancel out the noise and keep the faint detail.
After a certain point though, the CCD sensor gets saturated (i.e. the wells are full, or 'the buckets overflow'), detail gets washed out, so a longer sub isn't always better. It very much depends on the object in question, the camera, the amount of light pollution, the seeing etc.
So in general (this is just what I do, which is probably wrong) I take subs of a long enough length to capture the detail without blowing out any areas, then I take longer subs that blow out the brighter areas but capture more detail in the darker bits. Then I combine the whole mess, swear a lot ,wonder why I bother, get a very disappointing image, start drafting a 'for sale' thread, have a juice, try again and get that buzz when the data seems to be revealed out of nowhere, then start planning my next night....
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