As for why people want a personal assistant to shop for them when they could just use an app, think about it this way:
To get things (even online), I have to:
* Decide what *specifically* I want (brand, item, size, etc.)
* Decide where to get it from
* Obtain their website or app
* (often) Sign up for an account
* Enter a bunch of information to order what I want
* Follow up if it's late or wrong
With this service (or a hired personal assistant) I have to: * Decide what type of thing I want
* Tell someone to make it happen
Also, I wouldn't call Instacart or Expedia's interface "perfected." Thanks to the way the industry works there's still not a single website where I can say "find me the cheapest flights from point A to point B in date range X" and have it actually do so. With Instacart, I can't just punch in a natural-language grocery list and say "get me decent quality options for each, but make the beef grass-fed please." I have to go through a huge array of brands and potential sources for each item and decide what to get.The value proposition: People can fire-and-forget an order for anything. Someone else handles the details. People with more money than time -- a great market to serve -- prefer to trade the former for the latter. Cheapo McCouponClipper will sift through the apps individually.
Do you go to the grocery store and tut-tut people in line? Don't they know they can get batteries cheaper at BatteryWorld? Vegetables cheaper at the farmer's market? Windex cheaper at Bob's Industrial Cleaning supplies? Why are they at a general-purpose store with a larger markup?
But it doesn't matter. The incredulity of objectors who ask "Why don't you just install 20 apps and save some money?" will be superceded by people who just want to use the service.
I think what you, and the parent article, are responding to is that it's really hard to actually have an always on-call, fast-acting butler at your service.
Oh right, because that experience sucks mightily. I have this lovely full color screen that can display menus, location and delivery times, let me search by cuisine, choose various customizations, etc etc. Then a "magic" computer sends the orders to the restaurant via an already configured and tested system so they are expecting an order and can fill it quickly and efficiently.
Or alternatively, thanks to this innovative new startup, I can SMS to some random number and say "I want food or something do you have any burritos" and then have them text me back, etc, etc.
BUT WAIT says the new startup. IT'S NOT JUST BURRITOS, in fact it's not just food. You could ask for a burrito today and a flight to Cancun tomorrow, and you only have to put one phone number in your address book.
Aha, the real value proposition emerges. This startup uses their proprietary technology to know that Seamless or Instacart or Expedia exist already, and then they use it for me. Except it takes twice as long, without the UI/UX those services have perfected, and costs 30-50% more money.
Step one: Landing page
Step two: Corner the market on taking SMS messages and using them to punch orders into existing apps, using skilled college graduate US based labor.
Step three: VC/YC EXPLOSION
Step four: Profit