Here's a translation (by me) of that explanation into Ander-Saxon, a variety of English in which French, Latin, and Greek words and roots are replaced by native English ones.
Reckon what happens when somebody who speaks, shall we say, good Old English from the south of the land runs into somebody from the northeast who speaks good Old Norse. They can without fear pass on with each other, but the hardnesses in both tongues are going to get lost. So if the Anglo-Saxon from the South wants to say (in good Old English) "I'll sell you the horse that pulls my cart", he says: Ic selle the that hors the draegeth minne waegn.
Now the old Norseman -- if he had to say this -- would say: Ek mun selja ther hrossit er dregr vagn mine. So, roughly speaking, they understand each other. One says waegn and the other says vagn. One says horsand draegeth; the other says hros and dregr, but broadly they are onpassing. They understand the root words. What they don't understand are the wizardly bits of the wholespeech.
For a showdeal, the man speaking good Old English says for one horse that hors, but for two horses he says tha hors. Now the Old Norse speaker understands the word hors all right, but he's not sound if it means one or two, byspring in Old English you say "one horse", "two horse". There is no apartness between the two words for "horse". The apartness is carted in the word for "the", and the old Norseman might not understand this, byspring his word for "the" doesn't behave like that. So: are you trying to sell me one horse or are you trying to sell me two horses? If you get enough sittings like that there is a strong drive toward straightening out the tongue.
(I ran this past Professor Shippey in email.)