It has long been known that cooking vegetables will break down the vitamins and minerals. Alot of those vegetables they mention taste better when eaten raw anyway, or lightly steamed to soften them up a bit. I can't imagine cooking broccoli for 30 minutes, even though I do like it better steamed but still firm (it also brings out the color).

If you're not eating many raw veggies I suggest you make them a proper staple in your diet, and only lightly steam if you have to cook them.