Personally, I don't really think it makes sense to spend much effort preparing special food for the child at any age, so I tend to agree with Matthew Amster-Burton's guidance from his book Hungry Monkey.
When it makes sense, we reduce the salt content of our infant's food by mixing it with blander ingredients (mainly rice, potatoes, or perhaps beans that haven't been heavily seasoned). For less heavily salted food, we don't even go that far.
Our son's been eating that way since he was about 6 months old. When our doctor suggested slowly introducing solid foods between 4 and 6 months, we mostly gave him things like rice porridge with small amounts of food pulled from something I was cooking prior to salting or seasoning, but I now very rarely pull food aside except if I plan to use an unusual level of seasoning, and he's about 9 months old now.
Because of the way I cook, many dishes I make tend to focus on the natural flavor of the ingredient I'm cooking anyway, but I don't shy away from seasoning. I prepare familiar ingredients in several different ways anyway; even without an adjustment in seasoning, roasted vs. blanched vs. grilled vegetables will taste different.
The only seasoning other than salt that I'm a little cautious about is chilies, since they tend to leave a lingering burning sensation on the lips and skin that's uncomfortable for our son and most small children. So we don't give him chili-heavy food, but that's not to say he "never" consumes something with any chilies in it. Sometimes he quite enthusiastically eats things that have a touch of chili in them.
So, my answer is essentially this: when you're using spices in your own food, it's fine to introduce them to your child. No need to wait even as late as toddlerhood.
We haven't ever bought baby food other than a couple of Japanese products that are essentially soft, easily masticable crackers which we mostly use as between-meal snacks. So I can't comment on purchased stuff much.
But my thinking is pretty simple: We don't have the luxury of time to prepare completely separate meals, we don't really want to purchase special convenience foods just for him, and we want him to learn to adapt to the way we eat. Besides, pulling aside food before it's completely cooked sometimes results in harder to eat food because the vegetables may not become tender enough to eat without a little additional cooking time. I'm certainly willing to adapt food by chopping it more finely, using a mashing utensil, a blender, or mixing small amounts of heavily seasoned food with blander things.
2015 addendum After a few more years at this, I can say that both of our children went through a period of increased preference-driven behavior between age 2 and 3, but persistent exposure, cajoling and negotiation mean have resulted in children that mostly eat what we do, though they may prefer one or two dishes that we serve vs. others (my style of cooking typically involves 3-5 small dishes per meal, unless we're doing something like pasta). To be fair, our food has become a little less aggressively seasoned than I might have typically done 6 years ago, but my younger child just ate a ton of chili-lime spiced almonds tonight, so it's just a different percentage of the mix. I'm still a bit cautious about things involving heavy amounts of chilies, but both children will occasionally choose to eat some of those strongly-flavored things. Additionally, both children have markedly different favored vegetables and seasonings, and those preferences continue to change over time. We've also found that some things that might not go over well in one context are fine in another; the older one might reject mint or shiso leaves that are visible, but he'll eat mint chocolate ice cream or shiso/umeboshi furikake on rice. He'll eat a Japanese curry but rejects many Indian-style dishes.
