1. No EPA requirement what so ever, the only place in the world that the EPA means anything is in the USA, they did not build a "special" saw for that market.
Perhaps this will be futile, but I will try.
From Madsens, I believe they are somewhat familiar with chainsaws:
The Facts on Today's Pro Saws
Today’s pro saws, and all new hand held power equipment sold in the US, meets emission specifications set by the Environmental Protection Agency. We are often asked about these regulations and their affect on pro saw performance. The following are some questions and answers we've compiled on the subject.
Q: What does the EPA regulation do to pro saws?
A: The EPA regulation is complex, but basically today's saws are designed to produce less harmful emissions - less carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx). The amount each saw model is allowed to emit varies and is based on its power output. Large and powerful pro saws are allowed to produce more emissions than smaller less powerful saws.
This is a Husqvarna 575XP. It is designed using stratified charge technology. New versions of this saw also have a "self-adjusting" electronic carburetor. This is a step closer to what we believe will soon become electronic fuel injection or more accurately "electronic engine management."
Q: How do saw manufactures make saws that emit less pollution?
A: One way is to use less fuel in the air/fuel mixture. In short, the engine is run leaner. This creates some challenges for chain saw manufacturers. Lean running engines tend to be over-revved and they tend to operate at higher temperatures. Some manufacturers also fit their saws with catalytic converters. These devices are part of the muffler. They reduce HC emissions by burning fuel in the exhaust that didn't get burned in the combustion chamber.
Some of today's pro saws employ engines designed using "stratified charge" technology. In this design, a saw's transfer ports are filled with air while and air/fuel mixture fills the crankcase. During transfer, the first portion that enters the combustion chamber has no fuel in it. This is the portion that usually leaks out the exhaust port, so this helps reduce HC output. This is an effective design, with minimal impact on the performance of the saw. It is also very effective at reducing HC emissions. You will see more saws that employ this porting as new saw models are introduced.
EPA Saws Q & A
OK, this is interesting in that this specfically mentions Canada:
The Canadian government and manufacturers, having entered into a memorandum of understanding regarding emissions standards, also agree to comply with the emissions standards and test procedures cited in EPA regulations.
From this USDA publication.
http://www.fs.fed.us/t-d/pubs/html/02511204/02511204.htm
2. The line from the tank vent is to salvage fumes from the fuel tank and fuel in a failed tank vent situation/overpressurization.
OK, so what is the point of running these fumes into the carb if it weren't mandated since it can easily lead to flooding?
3. The same said line with a one way check valve is defeating the purpose of the tank vent, as the tank vent permits both vaccum and pressure to take place.
I prefaced this with admitting, "I am no mechanic". Does this valve allow the tank to vent to the atomosphere, the answer is yes or no?
4. Your "dealer" installed "check valve" is a two-way tank vent, you are correct it is an Echo part.
OK
5. Your "dealer" is messing with the warranty status of them saws before they go out the door.
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