442s are getting new traction packages and will return to run a faster Portsmouth service.
Not quite the full story I'm afraid - please pay careful attention to the wording of the article and note the use of the word "vehicle".
The 444s and 450s used on long distance / outer suburban duties are staying. These have a fleet size of 45x5 and 127x4 respectively which gives a total of 172 units or 730 vehicles
The 455s (91x4) , 456s (24 x2), 485s (36x5) and 707 (30x5) are the classes the new franchise holder will be getting rid of and in total come up to 157 units or 742 vehicles. Crunching the numbers actually shows the order for Aventra units produces a reduction in fleet size, 7 less units than with all the above mentioned classes in service - but because the Aventras are all 5 car units (thus giving a fleet size of 150), the number of vehicles goes up to 750.
So yes, as far as London suburban services are concerned all the units will be replaced by Aventras.
However outside of the London suburban area no new trains are being provided - only 'additional' ones that, as you say correctly state, will consist of 18 refurbished 442s(the remaining six 442 units have already been snapped up by an Open Access operator who wishes to run competing services from Southampton to London). Thus the Siemens built 444 / 450 EMUS and the BR era DMUs will remain under the new franchise.