Aren't all PSP games (Download only) playable on the Vita?
I think it depends how TheUltimateSword is meaning this.
All PSP games "Do" have to be downloaded to play on the Vita. You can't use your UMD's. However, some "I believe" have to be downloaded to the PS3 and then transferred to the Vita, while some can be downloaded directly to the Vita. So, I guess it depends on how he is meaning it.
It's not that some "have to be" downloaded to the PS3; the American PSV PSP emulator is crap compared to Europe's and Japan's. Plus issues with the PSN that still has to certify some games. Since we no longer have access to Media Go to download / transfer files, the alternative is a PS3 (when available). You could download any PSP game into it to transfer to a PSV; now, whether the game will work or not is a different story. But for example, MGS: POP and PW can be transferred and played despite the fact you can buy them on the PSV PSN~.