Maybe they ought to...... but the simple fact is (from what you said) they don't! If Korg does and you want that sort of thing..... you may have to go with a Korg sytnh (it's not like Korg's aren't good synths!!) If one company excels in a certain area, it's kind of ridiculous to complain about another company not excelling in that area........ one company cannot possibly excel in every area, I'm willing to bet that there are some things that Roland does better than Korg. Seeing as I'm a Roland user myself, I could probably name a few too. It's up to the consumer to decide what features they need more (I chose the XV-88 over something like a Triton because I needed a better feeling keyboard and better acoustic samples) So just look at the whole picture.
And YES, you can get more patches for whatever kind of music you want to do with the huge SR-JV libary of expansion boards, sure you have to pay for 'em.... but it is work after all to make patches and new samples. There's my $.02, hope it made some sense!
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Romans 6:23 For the wages of sin is death, but the gift of God is eternal life through Jesus Christ our Lord.