Most hostas are genetically diploid (chimera in leaf layers are 2-2-2). Hostas with the thickest leaves are often polyploid (4-2-2) or (3-3-3) or tetraploid (4-4-4) hostas genetically.  The advantage of a thicker leaf is improved sun and slug tolerance and being more rugged.  White center hostas with a thicker leaf are more sun resistant.  Tetraploid hostas often have larger blooms and the leaves are held more upright.