This isn't really going anywhere, so I'll make my last set of points. Relevant http://xkcd.com/386/.

> losing one's phone could mean losing keys, ID, wallet, etc.

Yes. It also means replacing them all is also only one step: getting a new phone and restoring settings from the cloud. Some comparisons:
Losing my keys:
Analog:
--4 with backups are a quick trip to a local Lowes or Home Depot, ~30 min, ~5 bucks
--2 without backups == I'm buying new locks. Same trip to Lowes, also installation time of an hour or so. ~$250 bucks. (also a good reason for me to go make the 30 min, couple buck trip to make copies now)
--1 car key. Trip to the car dealership. At least an hour, minimum $300.
Total: several hours, ~$600.
Phone:
--1 trip to T-mobile, cost of new phone.
Total: an hour, cost of new phone.

Losing my wallet:
Analog:
--3 credit cards, 1 debit card: ~15 min/card for calling and ordering replacements, > 2 days until a replacement arrives. Free.
--health insurance card. >30 min phone call. Probably more. Health Insurance has the worst customer service, a week before replacement. Probably free.
--Driver's license. Between 30 min and 6 hours at the DMV. ~$50.
--Clipper. Quick to order online, takes a few days to show up. $3.
--Safeway Club Card, Membership cards. Probably a trip and a few minutes per card. Probably free.
Total: > 1 week to return to normal. < $100.
Phone:
--1 trip to T-mobile, cost of new phone.
Total: an hour, cost of new phone.

The problem with these comparisons is that they compare losing keys or a wallet with losing a phone. I would argue from personal experience that it's much easier to keep track of 1 object than 3, but that's not exactly solid. The negative arguments might make more sense: comparing losing a phone in both situations.

Now, it is true that consolidation increases the consequences of a lost phone. It requires backup methods of personal identity, payment, and home access, which as I said before is true of both wallet and keys anyway. It is, however, much easier and quicker to recover everything lost: 1 trip and one restoration done in minutes or hours instead of requiring many trips over the course of many days. Replacing a phone is really easy these days since everything is stored in the cloud.

> Oh, and what would happen if you had your way and someone lost their phone?
"Oh well, lemme make a call and see if I can get a replaceme--oh, wait..."

Really? This is just obstinance. Do you really try to replace your lost phone by making a call with your phone? No. You go to a store or order one online.

>Replacing my ID, keys, and cards wouldn't be fun, but all of that would be a fucking pleasant walk in the park compared to replacing a phone containing all of those things.

I've lost a wallet before. That was a nightmare. Hours and hours wasted calling CC companies, the DMV sucks. A long time to recover. Keys are similar.
A few years ago I had a phone stolen. Remote wiped it, ordered a new one online and picked it up in store, life as usual an hour later. Not a big deal like you're making it out to be, and honestly not very much different than losing a phone today since you need proper backups in either situation.