To use your example, even USD in my pocket is more valuable than USD in paypal.

That's how paypal makes money- for instance- if I sell a product on eBay paypal always keeps the money due to me for about a week- for "processing" or w/e- during this time they invest it and make money on the float.

The difference between liquid dollars in my pocket and money locked up in paypal is not deterministic or fixed- the relative values fluctuate. The money locked up in paypal is analogous to a fixed time certificate of deposit, that's what I was saying in the original post.

I'm not sure what you mean by "no guaranteed exchange".

I disagree with the assertion that "the only source of value difference between coins in the two networks is the friction related to the technical operation of the peg".

One could make the argument that another important source of value difference is the degree to which people are willing to hold either currency.

Think about the recent trouble with Ethereum. If I created a peg while the Ethereum price was high, pegging BTC to Ethereum at the pre-DAO rate, I would take a hit and loose money if we undid the peg after the precipitous drop in Ethereum value- isn't that correct?