Both Swansea players featured in last weekend's 36-26 win over the Pumas when Wales recorded a fourth successive Test victory, but are replaced by Geraint Lewis and Gareth Thomas respectively as Graham Henry's side attempt to become the first British team to win a Test series in Argentina.
"Colin Charvis has played some big games this season, particularly against South Africa, France and Argentina, at Llanelli," Henry said. "But I have been disappointed by his performances out here. His form hasn't been great so that is why he hasn't been picked.
"It is a message that you have got to retain your form to keep your international place.
"Matt Robinson scored four tries against Tucuman last Tuesday but could not carry that form into the Test match. We'd like to come to consistency of selection on the right wing so it's not ideal to make a change again.
"It's a psychological thing with Matt and he needs to get over the hump of producing the same performances at test match level as he does below.
"An opportunity only comes once or twice and you've got to make the most of it. Gareth Thomas was originally the No 1 winger. He was probably our best player on the field against Argentina A when he knew he had to produce it to get back into the Test team.
"He was very potent, showing urgency and skill. At the top of his game, Gareth is as good as anybody."
Henry said Dai Young and Andy Moore had come close to selection at tighthead prop and lock respectively, but added "We are going into a Test match when we could make history by being the first Wales side to win an overseas tour against a top eight country. You don't take liberties with that. We have got combinations in the side worked out over eight Test matches this season and we don't want to break that down."
Henry announced he would name his 30-man World Cup squad on 28 June, two days after the Millennium Stadium opener against South Africa. "There is no point hanging about," he said. "The sooner we can settle the squad the better."
WALES (v Argentina, Buenos Aires, Saturday): S Howarth (Sale); G Thomas (Cardiff), M Taylor (Swansea), A Bateman (Northampton), D James (Pontypridd); N Jenkins (Pontypridd), R Howley (Cardiff, capt); P Rogers (Newport), G Jenkins (Swansea), B Evans (Swansea), C Quinnell (Cardiff), C Wyatt (Llanelli), G Lewis (Pontypridd), S Quinnell (Llanelli), B Sinkinson (Neath). Replacements: N Boobyer (Llanelli), S Jones (Llanelli), D Llewellyn (Ebbw Vale), D Young (Cardiff), J Humphreys (Cardiff), A Lewis (Cardiff), M Voyle (Llanelli).
n Wales were beaten by Argentina A 47-34 on Tuesday. They were behind 44-15 in the 50th minute, but the scrum-half Rhodri Jones sparked a revival during an entertaining match which had seven tries. However, the tourists left themselves with too much to do and paid the price for woeful ball retention and defence. Felipe Contepomi kicked 24 points to punish Welsh indiscipline while Arwel Thomas had a haul of 19 points before being substituted. The game was interrupted when a photographers' gantry, which had been commandeered, by 20 fans collapsed. Fortunately, there were no serious injuries.
Argentina A: Tries J Fernandez Miranda, Camardon, N Fernandez Miranda, Grande; Cons Contepomi 3; Pens Contepomi 6.
Wales: Tries R Jones, N Boobyer, Walne; Cons A Thomas 2; Pens A Thomas 6.