I think you'll find
It's fell by the wayside not weighside
(thefuckestuppest cheapened this, on, Wed 26 Aug 2009, 17:32, 2 replies)

Technically
it DID fall by the weighside - the American bastardisation has become the 'wayside', but the origin of the saying means to give up on something as when a carts load was weighed and was over the allowed weight, it was said to 'fall by the weigh side' as the cart had to stay whilst the horses were allowed to continue.
(dchurch bah, Wed 26 Aug 2009, 19:17, closed)

Actually
I haven't been able to find any sources which would bear your etymology out. More logically something was said to fall by the wayside when it literally fell by the side of the way. One suspects that before the 19th or 20th C carts weren't really systematically weighed to ensure health and safety for all concerned.
(Flocculencio Anything's possible if you're a robot, Thu 27 Aug 2009, 5:25, closed)

It
wasn't for health and safety (duh!), it was for taxes, and predates the 19th century by a long way. It's also of similar origin for "to get away Scot Free" - taxes were levied on those that didn't have enough land to grow bramble for the building of sea defences (it was considered impervious to sea water), if you failed to pay the tax or grow bramble, your ear was cut off. If you lived outside the boundries that needed to pay towards the sea defences you were said to have gotten away "Scot free" as the tax was imposed by Lord Scot in the 15th century, the same Lord that imposed the tax on the weight in the carriages of trade goods through the same area - I'm not going to mention the area as it's where I live (I'm the local historian for the preservation society - again, which I'm not going to name as it would make it too obvious).

I'm pretty sure he wasn't known for his stance on health and safety issues - I mean, where would he get a knife sharp enough to have someone's ear cut off?

If you didn't have enough to pay the tax, the cart was confiscated until you did - or simply confiscated forever depending on the contents.

It was possible to pay the tax in advance - many people did this so that they wouldn't get stopped and weighed. This backfired as most carts were stopped regardless of advance payments. Many were found to have a weight in excess of what they had paid for. When asked where their load was they were said to reply "it fell by the weigh side".

It's mentioned in a book I have here, and is mentioned frequently in the Russel Thorndike novels that are based around this time - with the correct spelling of "weigh".
(dchurch bah, Thu 27 Aug 2009, 7:52, closed)

If we're going to be the self-appointed spelling and grammar police
It should be "number of" letters, people, cockups etc., not "amount of".

Number of letters ... amount of mail

Fewer cars ... less traffic

How many pints? ... how much beer?

The content more than makes up for the writing, though.
(Vice Admiral Sir Charles Cockbrush KCB MBE DSO, who is finding it increasingly difficult to log into b3ta.com wants to duck your aunt and kick your puppy, Thu 27 Aug 2009, 10:36, closed)

I don't
recall even mentioning cars or beer.
(dchurch bah, Thu 27 Aug 2009, 11:20, closed)

Beer
It makes you forget things.
(Vice Admiral Sir Charles Cockbrush KCB MBE DSO, who is finding it increasingly difficult to log into b3ta.com wants to duck your aunt and kick your puppy, Thu 27 Aug 2009, 13:05, closed)

Forget
what?
(dchurch bah, Thu 27 Aug 2009, 13:10, closed)