I think the Silver Cross pram was used in much the same way as any of the state coaches are used at royal occasions. Purely for display purposes.
I'm not sure anyone has said this - maybe someone has - but actually I think the pram is all because of the venue of the Christening.
Bear with me . . .
Royal Babies are usually Christened in chapels in palaces. ie you don't see them arrive. This one is being Christened in a church.
OK so - MASSIVE traditional Christening gown.
Will it go in a car seat? - no. Too puffy and straps won't do up. Can't arrive by car then
Can she arrive in a car seat in something else and get changed? - umm not really will slightly ruin affect, especially as she will have to get changed to be driven back again and none of the public will get to see her in her Christening gown.
Well they could come on foot! That way the public get to see them. Great idea! Will massive Christening gown go in baby's normal buggy? Only if the straps aren't done up.
Can they get away with not doing the straps up in the buggy? Good God no they would be slaughtered for this wilful act of neglect.
Could someone carry Charlotte? Possibly. But maybe Kate wants to be the one to transport her and it is uneven ground and she will be wearing high heels.
Hey! What about one of the old prams? Baby can lie flat and won't need strapping in and there's plenty of room for that massive Christening gown!