Buttons don't look like anything until you apply textures to them (which is what the UIPanelButtonTemplate).
You can make your butons look like anything.
Lua Code:
local f = CreateFrame("Button")
f:SetSize(40, 40)
f:SetPoint("CENTER")
f:SetNormalTexture("Interface\\Buttons\\UI-ScrollBar-ScrollDownButton-Disabled")
f:SetPushedTexture("Interface\\Buttons\\UI-ScrollBar-ScrollDownButton-Down")
f:SetHighlightTexture("Interface\\Buttons\\UI-Common-MouseHilight")
f:GetHighlightTexture():SetAlpha(0.4)
You can also use your own textures and ther built-in tab templates.
Lua Code:
local f = CreateFrame("Button", nil, UIParent, "PanelTabButtonTemplate")
f:SetSize(40, 40)
f:SetPoint("CENTER")