Check the combat rules in the rulebook, Sweeping Advance requires that models are in base to base contact at the end of combat. Page 43, second paragraph under "Sweeping Advances & Consolidation".
For the second, without the rest of the article for context it's hard to tell what's going on. See rulebook page 45. Only the orks that are in base to base, or within 2" of other orks within base to base, with the enemy unit can inflict hits, and those models will be able inflict hits back to the orks.
EDIT: Ah,
http://belloflostsouls.blogspot.com/200 ... grots.html
You left out an important paragraph between those two you quoted. As per the pile in rules, the unit must pile into the grots because they were engaged in the assault turn. Then next turn the orks charge into the enemy unit in the gaps left after pile in - but as I pointed out above, only those who get into base to base, or within 2" of another ork in base to base, get to hit the enemy unit, and they can be hit back by the same models they are hitting (and at I3 will often be hit first). What the article seems to have neglected to take into account is that if the orks are in contact with say 2 models, then they can only kill those 2 models - the article seems to think that additional wounds spill onto the rest of the unit somehow, which is wrong as shown by the diagram on page 45 of the rulebook.