This is only a partial answer.

Here are some differences which I noticed when looking a the linked pages in your question:

Miner Reward. Forked blocks earned the miners a full reward (5 ETH + gas fees) while uncle blocks only earned them a fraction of that (4.1

Numbers As of today (July 7, 2017, 12.25 pm), there are only 15,584 forked blocks on the blockchain compared to 310,542 uncles. For some reason (that I hope someone else can explain), forked blocks are a lot less common.

Relationship Some forked blocks include uncles and others do not. Uncle blocks by definition all include one or two uncles.

Another big difference is that, after blockchain re-organization, forked blocks are excluded from the main blockchain (per the statement on the url you provided) while uncles can still be included / referenced, and that is in fact encouraged to help ensure that solo minors are not overly disadvantaged relative to mining pools.

Having noted all these differences, and done some web research, I still could not get to the core difference between both types of blocks. I hope others will help clarify further.

This is only a partial answer.

Here are some differences which I noticed when looking a the linked pages in your question:

Miner Reward. Forked blocks earned the miners a full reward (5 ETH + gas fees) while uncle blocks only earned them a fraction of that

Numbers As of today (July 7, 2017, 12.25 pm), there are only 15,584 forked blocks on the blockchain compared to 310,542 uncles. For some reason (that I hope someone else can explain), forked blocks are a lot less common.

Relationship Some forked blocks include uncles and others do not. Uncle blocks by definition all include one or two uncles.

Another big difference is that, after blockchain re-organization, forked blocks are excluded from the main blockchain (per the statement on the etherscan.io page you provided) while uncles can still be included / referenced on the blockchain, and that is in fact encouraged for a number of reasons which Vitalik explains in in this article:

Stale blocks in Ethereum can be re-included into the chain as “uncles”, where they receive up to 75% of their original block reward. This mechanic was originally introduced to reduce centralization pressures, by reducing the advantage that well-connected miners have over poorly connected miners, but it also has several side benefits, one of which is that stale blocks are tracked for all time in a very easily searchable database – the blockchain itself.

Having noted all these differences, and done some web research, I still could not get to the core difference between both types of blocks (i.e. forked and uncle). I hope others will help clarify further.