This actually makes sense if you think about resolutions... Vert res is much less important to the eye than horizontal res... The same way GT5:p is not true 1080p because it's made for a 16:9 screen yet stretches a 4:3 ratio to fit it, MGS4 could be doing the same thing for a 720+ resolution. It gives a solid framerate, people are less likely to notice, and the game still looks great.
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