Strange Policy from Dabs - wonder if they've had problems with questions such as "where's the manual?". Most other suppliers don't seem to mind. OEM is normally just bare bones components. No manuals, cables, instructions, software bundles, support, or fancy packaging (I did wonder at a DVD drive I bought recently which actually came in a sandwich, rather than an anti-stat, bag!).
If you're fully au-fait with what you're doing OEM will produce the same result as the full package at a fraction of the cost. If you're not, it won't!!
Additionally some item e.g. graphics cards will only include the card and a driver CD instead of extra cables (DVI) and a few games, DVD drives may only have the drive with no cables or fixing brackets and screws.