I recently had Ecofoam installed in the attic of my home.  At the time it was done I asked about venting the deck and was told that it wasn't necessary.  I have always been told in the past that this was important to the life of the roofing material.  I went with the recommendation of the installer who is a notable experiences company in our area.  Was I wrong to assume this was the correct way to install the foam?  I have to admit that our energy bill was considerable lower this past winter than it has been in previous winters.   The house was also a lot more comfortable and easier to maintain setpoint.  

I am now considering insulating the cathedral roof of my largest roof area when we replace the cedar with a more durable and lower maintenance product.  What should be the requirements for this new insulation?  Since this is a much larger area than my attic, is venting recommended here?  I am really confused about the venting issue.  Any suggestions or recommendations would be  helpful.

The effects on temperature of the shingles has proved to pretty marginal, especially on a roof with decent pitch, since most of the cooling of the shingles is from exterior convection currents, not cooling through the ~ R1 of roof deck& roofing felt into a hot ventilated attic.  The color of the shingle (& roof pitch when you get down to near-flat 2:12) has a bigger effect than insulate/uninsulated roof deck. 

The true value of vented roof assemblies is the ability to purge moisture (not heat) from the attic. But the effect of unvented insulated-roof attics on the moisture content of the roof decks will vary based on climate & insulation type- what's "right" for unvented cathedral ceilings will vary by climate zone.  Read this recent simulation project on this subject by Building Science.  While not perfect, it's way better than a WAG. It looks like 2-4" of closed cell foam in combination with spray fiberglass or cellulose would work in most of the lower-48.  In much of the US dense-packed cellulose or high-density spray fiberglass by itself may be the best bang/buck.  Cellulose has a higher thermal mass, is R-value stable over a wide temperature range, and may hold the performance edge in some situations (like places with many hours of 100F+ in summer or sub-20F in winter), but the noo-skool higher-density spray fiberglass (eg JM Spider) gives you a somewhat higher steady-state R-value at moderate temperatures, and may be a better overall performer in moderate maritime climates.

If you think you've put the wrong type of foam in your attic for your climate, moderate vapor retarders like vapor-retardent latex may  lower your risk. When you re-roof, putting down 1.3-3" (R10-R20) of panelized iso with factory-applied nailer deck above the structural roof deck will further protect & insulate the structural roof from condensation related issues.  Ecofoam comes in closed & open-cell varieties, and their vapor transmission properties are quite different despite both being excellent air-barriers.  According to BSC simulation you can get away with 2-4" of closed cell almost anywhere (but it's hard to detect leaking roofs until it's too late"),  but open cell alone can be an issue in colder/wetter places unless you have good air & vapor control on other layers.

I think the way you are talking about installing foam its a best way to install it and along with you are saving on bills so what else one can demand?