I generally keep mulch away from the canes/stems of roses and tomatoes, only because I heard it was good practice. But is it really?
Yes.
does it apply across the board, as this message sugessts?
Yes.

so when I put down 4 inches of mulch down in the spring and then my hostas, alliums, bleeding hearts come up I should pull that mulch away from the base of these plants?
or is this just for plants that are already above ground?

When they emerge, I would certainly pull that mulch away from the base of those plants. Even though they managed to push their way through the mulch, their roots didn't migrate upwards, and they probably needed to expend extra effort to push through all that.

Leaving the mulch against the base of those plants would invite the same problems with pests and disease as any other plant.

I'm going to disagree :-) You want to keep mulch away from woody stems and trunks, especially with a winter mulch, as these can hold too much moisture and create rots. With non-woody plants and in summer, mulching right up to the plant does not create problems.....although it can harbor insects, which can easily invade.

In colder winter climates, many plants are heavily mulched for additional cold protection, including upto and over the crown or any stems. Roses are often treated in this manner - in fact, bending over the shrub so it is more or less on its side and completely covering the plant with mulch is a common practice. Ditto for hydrangeas to protect latent flower buds from cold damage, although the mulch typically tends to be quite loose. And herbaceous perennials and bulbs are often totally covered with mulch in winter, regardless of climate :-)

One always need to be careful when dealing with absolutes when it comes to gardening -- there are very few that are universally applicable. The general rule if thumb is that it "depends" - depends on the plant, depends on the situation, depends on the climate, depends on the type of mulch. Or, never say never :-) There are typically exceptions to every 'rule'!

No.... (sorry gargwarb, I just had to say that ;-)

But really, There is no easy answer, There are so many factors, what you read is true but simplistic, I have an unlimited supply of "Finished Compost", I use that as mulch and I pile that up and around every plant and if "success is the answer to every critic", I couldn't possibly be more successful, I am truly blessed , and that is the way I do it.
With all that being said,If you use Bark or or some other kinds of mulch that could "injure" the seedlings, than Yes....that would be bad.
But it sounds like (from your previous thread about your compost), that you will soon have plenty of wonderful compost that you can use,that will be great.
BTW... Tomatoes stems LOVE to be surrounded by compost (comforted ;-)

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IMO we need to specify which type of mulch and which plants. If one is using compost on vegetables it's a different scenario from using shredded bark on perennials, trees, or shrubs.

I use a mix of compost and fine wood shavings over cardboard or newspaper and place the cardboard/paper as close as possible to the perennial stems, otherwise the weeds will come up next to the plant. I first carefully remove the weeds that are close to the plant, then cover the cardboard with a thin layer of mulch to hold it in place, and make it thicker further out from the plant.

One should never raise the soil level around trees and I think that means mulch as well so the mulch layer should be thinner near the trunk.

Compost on veggies is more a soil amendment and I think the plants can easily grow thru a thin layer of compost.

Thanks for the enlightening discussion, folks. It's my sense as well that the writer's "never touch a plant with any mulch" is, for some applications at least, a gross overstatement. My raised vegetable beds look very much like the pics posted by jonhughes. And gardengal's comments on winter mulch (hey, I'm in Minnesota) are also to the point. Gary

This is why I have more books, then raised beds.
Many writer talk about what is good for their zone, as if it is the whole world, it maybe for them.
I agree with jonhughes & gardengal.
I know that the only problem I have had with wet mulch on Blue berries & azaleas is that they root on the lower limbs(layering). Figs are always mulched, & covered with a dry mulch in winter like pine needles.
I am in dry(Summer & Fall) South Carolina so mold & fungi do not spread like the cooler Northern states do.

My mulch is almost always compost, so it goes right up to the stem of my peppers and tomatoes, spinach, and lettuce.