Really need both: 24-70 2.8L and 17-40 F4L

Does one really need both of these lenses? maybe one for portrait,and one for nature? just wondering.

I bought the 24-70 and then didn't think it was wide enough. I didn't have enough to get the 16-35, but read reviews that the 17-40 was good, so I went for it. I use both and I think with the 20D, the 24-70 is just not wide enough. On the 5D, it's plenty wide. So, you have to decide. I use them both for landscapes and portraits. Just depends how much bokeh I want or how much color. The 17-40 is amazing for me. The 24-70 can't be beat for a zoom for portraits.

On a 1.6 crop a 17-40 is actually quite close in range to a 'standard' zoom, just being a little short, so I think you should consider carefully what you need exactly. (it's like, 27.2-64)

depends on the needs. I could live with just the 16-35 and 70-200. I hardly ever like to shoot in the middle. Though for most people the 24-70 lives on their cameras