Ok, here's some thoughts about consumables from the perspective of an alchemist:
1) Flasks require Frost Lotus. Frost Lotus is rare and not cheap, anywhere upwards of 40 gold as of this writing. Most herb/alch combinations generally do not sell any Frost Lotus they find, simply because they get used themselves. The only way to acquire Frost Lotus, other then buying on the AH, is through farming, and it is generally more time-efficient to do dailies and purchase then to farm. Which is why they're expensive.
2) Some classes definitely see the most benefit from using a flask for every situation. Others... may not.
3) Case in point: Average flask prices currently are about 35 gold, with most of that cost in the FL (one FL makes 2 flasks). For casters, they *may* benefit nearly as much from using a combination of a +spell power and a +mana regen elixir. Compare: Frost Wyrm is +125 sp (at 35 gold). Flask of Pure Mojo is +38 mp5 (at 35 gold). You choose ONE of those, for 1 hour.
4) OR... 1 Spellpower Elixir is +58 sp (2-3 gold) plus 1 Mighty Mageblood is +24 mp5 (at 4 gold) also lasts for one hour. Total of 7 gold.
So... unless you are dealing with serious min/maxing issues, and ASSUMING 2 deaths in the first hour (therefore 6 elixirs - 3 of each), you are looking at 21 gold vs. 35 gold, and without consuming a rare drop, vs. consuming stuff that most herbalists should be able to give away.
I'm just suggesting that especially for content that *should* be on a farm status, it may be sufficient to use two elixirs instead of using a flask, at a significant cost savings.