Riddle me this

OK, so just out of curiosity, can anyone explain why my kid won't eat a bite of her dinner until she gets ALL the stuff that is being served? Like tonight -- for dinner, I made her beef, crackers & pretzels (yeah, yeah, I know. I'm out of carb ideas. So sue me), raisins, and grapes. I served it all up except the grapes. She asked for the grapes. I told her in a minute. She got upset and refused to eat anything else. I told her to get started on the rest of the stuff and the grapes would be on their way. Fussing ensued until I gave her her grapes. At which point she ate everything in front of her and asked for seconds, and thirds, on the grapes.

Is this a 3-and-a-half year old thing, or just my kid?

Enquiring minds want to know.

P.S. The grapes were tasty, I admit. We're on a roll over here. Do grapes actually have any nutritional value, or are they just nice sweet cold treats? Either way I'll keep serving them to her, and I'm glad she likes them, but I'm curious. Grape research underway, I'll report back.