I can't see any obvious reason why loading DPTR using mov dpl,# and mov dph,# should work any differently.

Otherwise, if you want strings in a fixed area, why dont you do the following:

.ORG $8000
string1 equ $

.ORG $8100
string2 equ $

Also for generality, why don't you arrange your print string routine so it takes dptr as the pointer?

mov dptr,#string1
call pstring

mov dptr,#string2
call pstring

or another method is to embed the strings into the code like this:

call pstring
.db 'hello there!',0
.....
where the pstring code expects the string to follow - it gets the return address off the stack and uses that to get the pointer to the string. When finished, it pushes the return address past the string onto the stack.

Whilst this doesn't solve your problem, it may induce some thought!