Bro, 3 reasons:

1. If he is that good, err.. if SAF trusts him, he would definitely been given more chances than Edwin considering Edwin's age.

2. And if he is that good, oops, if SAF trusted him, Edwin doesn't have to play until age 40. It's quiet similar to Lehmann - Almunia situation in Arsenal but it just that Wenger was more trusted Almunia than Lehmann (other way round compared to Tommy's situation). There might be a factor why SAF still uses Edwin as first choice GK (One of the reasons i can think of is, like i said (did i? can't remember) partnership with Nemanja and Rio was as smooth as traffic condition in KL without traffic jam, literally)

3. If SAF trusted him to be the replacement of Edwin, SAF would not purchase Lindegaard and his interest on Sketenburg or De Gea. Let's take example situation before Lindegaard is here.

Before:
a) VDS
b) Tommy
c) Amos, Ben - A promoted GK from academy proved that we did not have to purchase anyone due to VDS's to be the only trusted first choice GK with a very good backup goalkeeper like Tommy behind VDS

After:
a) VDS - Still the first choice despite the age
b) Tommy - Still warms the bench seats.
c) Lindegaard - ??? Donno what he's doing here... currently, think about it. SAF has better plans ahead.
d) Another GK rumours - Why do we need another goal keeper

Next season probably:
a) Stekenburg / De Gea or Lindegaard
b) Stekenburg / De Gea or Lindegaard.
c) VDS - Retired.
d) Tommy - Where the heck he want to sit down at? Unless out for loan n another club or a permanent move for good. Aston Villa or Everton might suits him well.

edited: Sketenburg not Stekenburg. Damn why our GK/future GK's name so damn long one and hard to spell one?