Reproduced in v.10.0.0 under Win7 x64. In v.8.0.4 only *major* logarithmic frame ticks change their thickness, but not *minor* ticks.

Let us elaborate. First of all, in v.10 the logarithmic tick specifications are generated dynamically when the plot is rendered by the FrontEnd by calling ``Charting`ScaledTicks`` and ``Charting`ScaledFrameTicks``:

 LogPlot[x^2, {x, 1, 3}, Frame -> True];
 Options[%, FrameTicks] 

> {FrameTicks -> {{Charting`ScaledTicks[{Log, Exp}], 
> Charting`ScaledFrameTicks[{Log, Exp}]}, {Automatic, Automatic}}}

Here is what these functions return (I have shortened the output for readability):

 Charting`ScaledTicks[{Log, Exp}][1, 10]
 

> {{2.30259, 10, {0.01, 0.}, {AbsoluteThickness[0.1]}}, 
> {4.60517, 100, {0.01, 0.}, {AbsoluteThickness[0.1]}}, 
> {6.90776, 1000, {0.01, 0.}, {AbsoluteThickness[0.1]}}, 
> {9.21034, Superscript[10,4], {0.01, 0.}, {AbsoluteThickness[0.1]}}, 
> {0., Spacer[{0, 0}], {0.005, 0.}, {AbsoluteThickness[0.1]}}, 
> {0.693147, Spacer[{0, 0}], {0.005, 0.}, {AbsoluteThickness[0.1]}}}

It is clear that the thickness specifications are already included and have higher priorities than the `FrameTicksStyle` directive. That is the reason why the latter has no effect.

So this behavior reflects inconsistent implementation of ``Charting`ScaledTicks`` and ``Charting`ScaledFrameTicks`` which should NOT include styling into the tick specifications they generate. It may be called a bug.