"What does it matter if the slabs can be openned?"

I guess one has to have an understanding of what constitutes a "slab". If the the item (coin, chip, baseball card, stamp, etc.) is merely housed in a snap-type plastic holder; in my opinion it's not a slab. A true slab is sealed in the plastic holder and the only way it can be opened is by destroying the sealed case it is housed in.

As Barry H. has stated, if the case can be opened, then another chip of inferior grade can be inserted which negates the original grading opinion.